Graphics and Sound
Thief's graphics are based on Looking Glass' own in house engine. While they do feature some slick lighting effects, overall the graphics are a mixed bag. As I mentioned, the treatment of light and shadow is fairly well done in Thief, which is important because staying in darkness is a key part of the game. Also, the textures are quite detailed when it comes to the setting and background but the characters and monsters do look a bit dated when you compare the game to Half-Life, SiN, Unreal, and many other recent first person shooters. Not to say that the graphics are ugly; not at all. Let's face it: just about every first person game today has pretty good graphics. So if we were to grade Thief's graphics on an objective level I'd give it a B, but if we grade on a curve, the grade goes down to perhaps a C. The bottom line is that Thief's graphics get the job done, but they're probably nothing to write home about.
The sound engine of Thief is truly the masterpiece of the game. You'll need a 3D sound card to get the most benefit, but even if you don't have one, strapping on headphones is like stepping into another world. The sounds of footsteps carry down cramped hallways. You'll hear water dripping in dank basements and dungeons. A startled guard crying out "who's there" can be enough to stop your heart. All of these aspects come together and combined with 3D spatial effects, it has an incredible effect. Just play up through the prison level and listen to the pathetic echoing moans of the prisoners and anyone will be convinced: Thief has probably the best sound of any game available today.
Better move that body
The Thief engine also features some nice physical effects. All the major elements play a role, including wind, fire, and water. You can use water to douse torches and fireplaces and create more hiding places. Whip out a flame arrow and you can re-light those flammable torches if you like. Heavy objects like dead or unconscious bodies can affect the environment; if you drop a guard in a doorway you'll have to pick him up and move him in order to close that door again.