Mario Bros was the next game that Shigeru Miyamoto and his past colleagues had made after Donkey Kong, in which debuted the now iconic Nintendo-exclusive characters who are Donkey Kong and Mario (formerly known as the less-impressively-named Jump-Man).
Like Donkey Kong, this game has the portly antagonist negotiating small levels, called phases here (as in phases of building projects; this game was made during the boom of Japan's construction industry). His brother, Luigi, also makes his debut in Nintendo's hall of fictional characters, albeit he was initially a mere colour-palette-change of Mario.
Instead of having the player chase after a big simian and his lady hostage as a blue-collar worker whose skills of his trade are not clear (other than acrobatics at negotiating hazards), this game had Mario working as what would later become his full-time job as a plumber of sorts. Mario Bros, in hindsight, laid the foundation of the establishment of Mario and Luigi's character designs.
However, instead of clearing pipes by conventional means, e.g. with a monkey wrench and lots of duct tape, his job appears to be far more dangerous than what one would expect regular plumbers to perform. He has to remove critters that appear to have infested the phases. Every phase consist of the same arrangement of platforms, which always number the same and are situated on the same elevations regardless of the phase in play, of which there are several dozens. The player character can move from one vertical edge of the screen and reappear from the opposing edge at the same elevation. (The critters can do the same too.)
The aforementioned critters appear to be using the pipes as a loitering ground to wander about aimlessly. They come into play (figuratively speaking, that is) from the top pair of pipe outlets (which are conveniently coloured bright green - a gag caused by limited colour palettes at the time and one that would later be repeated in Super Mario Bros). The critters would proceed to move in a single direction (either right or left), and will continue in the same direction after they drop onto a platform below the one that they were on. They will, however, change directions after colliding with other critters, or the player characters (which is, of course, harmful to the latter).
To defeat critters, the player character has to jump and punch the platform that the critters are on, at the very same spot that they are moving over. This generally causes them to flip onto their backs, as well as stopping them completely. The player character can then run and/or jump up over to them, and, humourously enough, kick them out of the level, effectively banishing them from ever loitering about again.
(Coincidentally, Mario's simultaneous jumping and punching animation would later become a habit of sorts in later games starring him and his brother.)
The collision detection mechanic that is used to accommodate this game design appears to be adequate enough such that timely jump-punches will connect, but not so generous such that some skill is still required on the part of the player.
However, the critters had been designed so as to not make them so easy to remove. There are a few variants of them: the initial one is the (relatively) slow-moving tortoise (who would later become the iconic and idiotic Koopa enemies in Mario's later games), the next will be the tougher crab that needs to punched from below twice before it flips over (and punching it the first time around makes it angrier and faster) and the one after that is a fly that hops around (making it more difficult to time and punch from below).
They may all seem idiotic, but the game includes some penalties for not getting to flipped enemies quickly enough. Eventually, flipped enemies will upright themselves if not kicked out of the screen and they, consequently, becomes faster as a result (as is denoted by a change in the colours of their character models). Failing to kick them out twice in a row will cause them to achieve their fastest movement speed, which is indicated by a colour change to peculiar but still intimidating pink. In addition, to sort of instill more challenge into every phase, the last critter will also gain the pink state.
However, it has to be mentioned that the fly-like critter does not appear to undergo any color changes at all, regardless of any circumstances. It does however gain the usual speed boost if the player character neglected to remove it after it has been flipped. This inadvertently makes the later phases harder, as the player may not be able to get to this particular enemy in time due to the chaos of flipping over so many other critters and dodging prematurely conjured fireballs. The fly-like critter also does not appear to gain the usual tremendous speed boost for being the last one in the phase, suggesting that the developers may have included this type of critter late during development but did not properly incorporate it into the game.
A mechanic that would later be borrowed by Wrecking Crew - among other game designs that would also be borrowed - concerns an occurrence that happens if a player happens to dally on the platforms of a certain elevation for too long. A green fireball with a sinusoidal trajectory will be conjured on the same elevation. This fireball, of course, hurts Mario. In addition, during the later phases, a red fireball with a slower but different sort of movement will also be conjured; this one bounces around the level instead. Obviously, these conjurations were meant to increase the challenge of later phases even further.
Perhaps the more interesting aspect of these fireballs is that they have been designed so that experienced players can still dodge or even defeat them. A quick player will be able to jump over or run under them, or even time an uppercut to warp the platform that they are about to come into contact with (or coming into close proximity to) and extinguish them for some bonus points. Of course, the player would be playing with fire here (pun intended), as the fireballs would spawn at ever increasingly faster rates as the player expends more time for a phase.
In addition to fireballs and critters, a couple of mobile objects that can be optionally removed from the screen also spawn into the phase. The first is apparently an Icicle that slides around and appears with increasing frequency in later levels. It will eventually stop and freeze over a platform, starting with the lower ones. This places some pressure on the player to remove them whenever possible, as slippery platforms are hardly reliable to move on; there is also the incentive of bonus points to be gained from removing them out of play.
The other object is a Golden Coin, which the player character can run into or punch in order to obtain some bonus points. (Incidentally, the model for this coin would later be used in the Super Mario Bros games for the NES.)
Coming into contact with fireballs, critters and icicles results in the player character being incapacitated, and thus losing one of his "lives" (though this reviewer prefers to think that this is his chances given by his employer before he is unceremoniously laid off). Additional lives, up to a (rather paltry) maximum of three, can be earned as the player reaches certain score thresholds.
Unlike other games (at the time) where losing a life forces a restart of the level, the player character simply respawns at the top of the screen, floating downwards on an oddly (and likely hastily designed) purple platform, from where he can survey the current situation from a safe vantage. However, apparently a player can choose to indefinitely drag a level this way, so the developers had saw it fit to have the platform degrade and eventually force the player into action.
To assist the player in clearing levels of blissfully dumb vermin, there is a special, small platform (which is represented by a block with the onomatopoeia "POW") that can be punched to momentarily shudder the entire screen. Any critter (and fireballs) who happen to be moving over any platform at the time will be stunned and/or flipped. The POW block also acts as a handy, if rather narrow, additional platform. However, each subsequent punching of the POW block diminishes its size, until it disappears completely.
(It is worth nothing here that the POW block would return in the Super Mario Bros iteration for the SNES, where it has a similar function.)
The POW block is fortunately restored every four phases, a stretch of which ends with a bonus phase that populates that level with coins instead of critters to be smacked. This bonus level also introduces what can be said to be no more than a palette change for the look of the level.
Every subsequent phase increases the number of critters that spawn into the screen (via the top pair of pipes). Additional AI scripting will also be added to the critters, giving them new and somewhat random behavior, such as changing directions after dropping onto a platform below. This serves to increase the challenge of every subsequent phase, which otherwise would seem deceptively similar to the previous one. However, the core of the gameplay ultimately remains the same: remove every critter that spawns. The game can get monotonous, if not for the increasing difficulty.
The game, as mentioned earlier, has satisfactory collision detection for the purpose of jumping and punching platforms. However, jumping up and over ONTO said platforms is an entirely different matter. There appears to be little in any way to adjust the protagonist's trajectory when he is up in the air; only the directional button presses that were made at the same time as the jump mattered. There is no ability to add after-touch to jumps (which was a criticism that would be addressed in games made by Nintendo in the future). As such, players can end up watching helplessly as Mario descends on a critter (or fireball) that the player could not dodge way ahead in time.
Perhaps the most interesting aspect of the game is that it has a two-player mode, which places two player characters (that is, Mario and his brother, Luigi) in the same screen; for a 1983 game, this was quite the rarity. This mode can be played cooperatively - or competitively (although the latter choice of gameplay can result in more than a few raging arguments).
The player characters can apparently affect each other in a physical manner. A player character can collide with the other and block each other's path, jump and punch the underside of the platform that the other is on (thus causing him to be momentarily stunned) and also jump off each other's heads (which can be practically used to hit a platform that is two levels higher than both players are currently on). There are a lot of tricks that a tightly knit pair of players can pull off, possibly even those unintended by the developers. However, there are also just as many ways for a couple of misfits to aggrieve each other.
The latter case, unfortunately, can end with one player permanently being removed from the session, as each player character has his own separate pool of lives. When that happens, the session pretty much regresses to single-player mode and the co-op charm is lost. This mode could have been more fun if more tangible incentives for effective co-op play had been introduced to the players from the start. As it stands, for this reviewer, the only game design decisions that suggest that co-op play is the way to play the game is its title and its demos.
Pausing the game apparently removes all moving models from the game, which doesn't help the player much in planning his/her next move, giving the impression that the pausing feature is really only there for the convenience of toilet breaks.
Most of the music in the game occurs during the start of the level, which is usually accompanied with an 8-bit-filtered stanza from one of Wolfgang A. Mozart's more famous symphonies. However, in contrast, a peculiarly long pause ends every successfully completed level, but this is just a minor complaint. The pause could, in fact, allow the player a sigh of relief, as some of the later levels can be quite hard.
The design of sound effects for this game is intended to make sure everything happening on-screen is accompanied with a distinct sound clip. Unfortunately, while every occurrence, from the player character jumping around to critters falling on platforms, has a sound clip of its own, there can be plenty of things occurring on screen such that certain sound clips inevitably fail to play, with the cause likely being the limitations of the NES. Relying on the sounds of the game for indications of any occurrence is not recommended.
The graphics, fortunately, compensates for the sound effects. It was as what can be expected from very early NES games made by Nintendo: terribly simple, but effective enough at what they are supposed to do. Disregarding the weird colour palette choices for models in the game (as mentioned earlier), the player only has himself/herself to blame if he/she failed to notice something happening on-screen, because every occurrence has a clear visual indication and/or animation.
In conclusion, Mario Bros can be seen to have laid the groundwork for the more acclaimed Super Mario Bros games, if its features that made it into the latter are to be considered. Yet, these very same features are what made it fun in its own right.