This reviewer had the misfortune of having missed the vanilla version of The Second Encounter, but an offer of full trial for this game on Steam helped this reviewer keep up with the times (with respect to the Serious Sam franchise, of course).
This HD version of the Second Encounter is essentially the original version made prettier with some latter day graphical effects. The original version - and this one - continues from the cliff-hanger in Sam "Serious" Stone's mission in the first game. To put it simply, Sam has suffered a snag in his plans to defeat an evil alien warlord and has to go back further in time to sort things out - meaning that he has to kill even more monsters in vast new levels.
Speaking of monsters, there were a few new ones that were introduced in the original version, with the highlight being the Cucurbitoes (which are too hideous to describe and, suffice to say, are nasty in close combat). There are also a few bosses which were introduced for Sam to pulverize, though they still perform much like the ones in the first Serious Sam (i.e. they practically root themselves to a spot and spam attacks). All these enemies that debuted in the original The Second Encounter have been given graphical improvements together with the original ones.
Monsters now have more detailed textures that allow the tacking on of location-sensitive decals (namely wounds that they incur), in addition to updated animations and models for both motion and death throes. (The Gnaar in particular receives rather insulting - to it - scripts for the gory partitioning of its body upon death.) They also obtain new effects for the projectiles that they fire, which makes dodging them easier for player characters.
The monsters also gain updated sound clips, but, to this reviewer, the improvement in their quality is not very significant, because they were good enough already and served their purpose well (which is to indicate to players what the monsters are about to do). They still do, though they certainly sound crisper. Some are actually more hilarious than ever, such as the servo whine that the Bio-Mechs emit (despite hardly being mechanical at all).
Not to be outdone, Sam has also gained upgrades for the aesthetics of the tools at his disposal and other stuff that he has, starting with his player character model. The confident smirk that the developers have always wanted to plaster on his mug is now there for players to look at.
The Sniper Rifle, Flamethrower and Chainsaw had been added in the original version of The Second Encounter. They are still very effective at what they do, if not more. This is especially the case for the Sniper Rifle, whose user now benefits from the improved graphics that makes faraway enemies much easier to spot and target. The laser add-on, however, is only there for cosmetic flair (albeit a pretty one). Similarly, the Chainsaw now benefits from revving animations and updated sound clips, making it more of a joy when used to squelch enemies that get too close.
(However, this reviewer has to note that the Chainsaw is still quite an inappropriate weapon to use when mobbed by monsters, especially those that are tougher and faster than Gnaars. Moreover, the minor issue of some weapons being far more useful than others is still there, unresolved. In fact, the Sniper Rifle would be joining the small club of actually all-round effective weapons in this game franchise.)
The Flamethrower also gets a face-lift, but more importantly, its new updated conflagration effects also extend to enemies that have been ignited by it. It is now easier for a player to conserve ammo by identifying burning enemies and letting them die on their own.
The levels are pretty much what have been included in the original version, but with new objects added in to take advantage of the upgraded Serious Engine, such as torches and luminescent objects. The designs of the levels have also been changed to accommodate the new polygon counts. As far as this reviewer knows, there are no glitched surfaces that players can perch on for some positional advantage that was not intended by the developers.
The already impressive sky-boxes have been enhanced even further; there are now foreboding eldricht storms to look at, lazily floating snowy clouds and other visual designs that improved over the essentially static atmosphere that bounded the skies of the levels in the original The Second Encounter. (Of course, the player won't be doing much sight-seeing though, as there is quite a lot of fighting to participate in.)
It is also much easier to spot pick-ups and power-ups in the game now, likely due to zealousness on the part of the developers in applying HD properties to everything in the game. This also meant that secret areas are not so secret anymore, due to the sparkles that the pick-ups emit and their self-contained lighting properties (i.e. they can be seen very well even in dark areas).
In addition, there are new character models that can be used to replace Sam's default model. As a matter of fact, there is a female version of Sam as well, complete with her own sound clips for battle. These were all likely the prototype models for Sam that were mulled before the release of the original Serious Sam, and may have been pulled out of the closet for inclusion in this Serious Sam HD game.
However, it has to be mentioned here that the quips and one-liners that Sam makes in the campaign still use the original, heavy-baritone male version. It may be a bit of a disappointment to some. Furthermore, all of the models practically share the same animation files.
The music has also been updated to include tunes from more contemporary bands, most of which are metal in theme. Although they fit the theme of the game and the current situation well, the player, like in the original Serious Sam, won't be doing much listening to music when the din of battle is all around them.
It cannot be denied that The Second Encounter has benefited from the graphical and audio spruce-ups. There are also substantial additions in the form of new content that adds to the gameplay, though the worth of this new content would not be something that can be agreed to universally.
To the developers' credit, there are some new multiplayer modes, namely a couple of new co-op ones. One of them, Coin-Op Co-op, addresses a minor gameplay issue from the previous non-HD games, which is the limited number of lives that a player can have for sessions with any game difficulty (and the limited lives mutator). Players can now earn extra lives by racking up their scores.
This mode, which is an alternate take on the vanilla co-op mode, takes advantage of the new difficulty scaling, which drastically changes the number of enemies that spawn into play whenever the number of players changes. There are now more monsters for everyone to slay, but this new system still does not address the problem of having very experienced players plowing through most of the mobs and hogging most of the kills. Down and out players, like in the sessions with limited lives in the original game, have no choice but to quit the game and forfeit their scores (which can count towards some Steam achievements, at least for the Steam version of this game).
The other co-op mode is Survival Co-op, which places players in (relatively) small arenas that do not give as much room for maneuvering as that provided by the campaign maps. Supplies are also spawned in at a much slower rate, and every player appears not to get a 'copy' of the same pick-up as he/she does in the regular co-op mode - meaning that they supposedly have to learn to share. Unfortunately, even the most tight-knit team will have trouble planning their sharing of supplies, as enemies are spawned in very quickly. The spawning always occur on a fixed schedule, but at slightly randomized locations.
This means that if the team is not fast enough to remove the incoming threats, they will inevitably be mobbed, thus ruining any cohesion that they have as a team. As the effectiveness of the team in this mode depends not just on their skill and experience but the connection stability of the session as well, a slight lapse in this will render players helpless while the monsters still get spawned in anyway.
Moreover, some arenas are designed such that players appear to have a severe disadvantage: for example, there is a map that has one too many hill crests that provide incoming enemies cover, and another that hems in players in a claustrophobic environment while they are being hunted by Kleer Skeletons. Both of these maps do not have much in the way of ammo supplies. They are not impossible to beat, but this reviewer has the impression that the game designers had not tested this mode thoroughly.
Still, they are there to be bested, and the rewards are some achievements that can be some of the toughest that digital game consumers can ever work for.
In conclusion, while this game mainly recycles one of the previous Serious Sam games into a shinier form with little additional features, its gameplay is still a blast and may have even been enhanced by the face-lift. A few new additions to the formula of the game seem a bit unrefined, but they are still satisfactorily functional and fun.