Thief II's gameplay and theme may be quite alien to many digital game consumers of its time, so it was wise for its developers to include some exposition of sorts that revealed to the more unfamiliar of players the backstory of the game, the travails that its titular protagonist has endured thus far and what is in store for him.
The user interface, from the menus to the in-game HUD, is designed in a subtle manner, as befitting the theme of the game. The HUD follows FPS conventions of the time, but in particular shows the most important of information (e.g. the protagonist's health, his currently equipped items and supply of them, and his very critical light gem) in a space neatly tucked into the bottom of the screen. There are no flashy, attention-grabbing icons that would distract the player from whatever else happening on-screen, which is good as being observant is very important in this game.
The player takes on the role of Garrett, a master thief whose murky past and rebellious demeanour has driven him to take on a criminal career of stealing the riches of the opulently wealthy. This is a plenty intriguing protagonist, as do some other supporting characters which add to the plot of the series. For the purposes of preventing the mention of any spoiler, this reviewer would only say that the characters in the Thief series and this game are certainly not the usual archetypes that one would find in a game with typical medieval fantasy themes; this is certainly refreshing.
In keeping with the theme that is suggested by its title, the game rewards the more careful and sneaky of players with plenty of delectable trinkets for Garrett to swipe. Getting to these require overcoming hindrances like mobile enemies, hazards and traps in the game. In addition, there is a murky conspiracy involving a certain extremist faction in the game that Garrett has to involve himself in.
The game starts in proper with a small section of the first level dedicated to a tutorial of sorts. However, the tutorial does seem to be a bit short on details other than the basics of movement and the use of most items. Afterward, it is up to the player to figure out a way past obstacles that he/she has not encountered before, often with few clues and hints. It also has to be mentioned that being an expert burglar, this reviewer would have expected Garrett to offer some monologue of sorts to ease the player through unfamiliar puzzles. Yet, such moments in the game are scant few.
Thus, it can be said that the game is quite difficult, especially for beginners, who will find even the easiest setting to be quite a challenge (the higher settings gradually remove aid like maps and certain items from the player). The player will learn the hard way not to trail enemies too quickly, not to touch them when they are too close and to stay out of the light (and skulk through the oppressive darkness without visual enhancement of any kind).
Part of the difficulty of this game is guessing how the AI-controlled characters would behave. Many enemies use the same AI (the patrolling sentry AI), but with variations according to the level currently in play and their nature. Human guards tend to share information on their respective patrol paths and would notice any colleague who happen to be missing (usually from the player's dastardly actions), thus resulting in tense moments where they walk into the room that the player thought they would never go into after having observed their patrol patterns from the shadows and removed one or two guards who were assumed to be the only ones privy to these patterns.
Spooking such guards with clumsily performed actions like mistimed dashes from cover-to-cover also renders them alert virtually indefinitely (especially on the more difficult settings). Alert guards are much, much harder to remove, as well as react faster to further disturbances.
(Incidentally, such behaviors can also be exploited to get guards away from their usual patrol patterns. This can be quite a delight for players with great patience.)
On the other hand, inhuman enemies behave in less expected manners. The more ghoulish, being the restless or listless spirits that they are, tend to be either more alert or more oblivious respectively. The feral generally moves much faster and have better hearing, while automatons tend to have terrible hearing but are generally much tougher to tackle.
Needless to say, the Thief series has some of the most sophisticated AI designs of its time, and Metal Age is no different. The developers made use of the Thief IP's intriguing backstory and themes to craft some of the more challenging enemies that digital game consumers would face.
Mission and level designs are also hallmarks of this game. Many levels have puzzles, from simple ones to those that require quick timing and the use of a few different tools available to Garrett in one go to complete. The ones that are optional to solve are the highlight. These are devilishly clever puzzles, the presence of which only the observant and curious would realize, and the solutions for which only the persistent would discover (without resorting to guides or FAQs, that is). These puzzles would then yield deliciously unique-looking baubles that sell for much more cash on the black market (more on this later).
Yet, even after securing a mountain of loot that Garrett could not possibly stash into his tunic without making a huge racket and also completing the mission objective, the fun (and tension) does not end there. The player will have to extract Garrett from the crime scene, which is sometimes easier said than done as achieving certain objectives result in the level being repopulated with fresh, very much alert enemies.
It is therefore fortunate that the controls are designed competently as is required by the gameplay (which was quite unique at the time). Garrett has a few speeds of movement: a pell-mell run, a casual walk, a sneaking pace and a slow crawl. The two slowest speeds may be a bit too slow for effective stealthy take-downs of mobile enemies, unfortunately (though they make next to no appreciable noise). Also, unfamiliar players will have to be warned here that Garrett's running momentum do not transfer well to his jumps, so leaps of faith often end in miserable failure.
To provide some sort of worldly assistance to himself (& the player), Garrett will sell off any loot obtained after completing a mission on the black market (often for quite a pittance of prices, but he is the sort of thief who would not complain as he happens to do what he does for the thrill of it). Equipment choices range from the default blackjack and sword to handy items like vine arrows (and other types of arrows) and healing items. However, being the contraband that they are, many of them are not cheap.
Fortunately, the game is completely playable using only the blackjack and sword, to the credit of the wise developers of this game. The other gadgets only make thieving work more expedient, but are not absolutely required for the achievement of any critical mission objectives. (However, they will be needed for higher difficulty settings, which require the player to gather certain amounts of loot, as well as certain enemies that cannot be defeated using the default weapons.)
If there are any drawbacks to this game, they would be the graphics. The game has decent graphics, but the lighting is terribly subdued and the shadows are very, very dark (making them as much a hazard to Garrett as they are to enemis). Furthermore, in-game models are inadequately designed (e.g. strange bodily proportions, repeated models) and slowly animated (especially the human guards, who seemingly lumber). This makes them difficult to distinguish from inanimate objects, especially from afar, unless the player uses Garrett's mechanical eye to scout them out.
The audio, on the other hand, does a better job at supporting the gameplay. It does a decent job of alerting the player of any enemies in the vicinity, often through their varied (& sometimes amusing) monologue, (even more interesting) dialogue and their footsteps (which can be really loud, depending on how near they are and the surface that they are moving on). The voice-acting is also quite good, with the exception of a few characters whose voices are really grating (the automatons' and the main antagonist's, in particular).
In conclusion, Thief II: The Metal Age does a good job of preserving the reputation of its ground-breaking predecessor. It may not offer any new pleasant surprises, but it does build on the reputation of its predecessor and proves - yet again - that stealth-oriented gameplay is a feasible proposition.