It does a couple of things better than just about any game. The first of which is that it's one of the most embodied first person games I've ever played. This is to say that as a player, one feels keenly aware of one's own physical presence. How visible and audible the player is is almost the entire game, and the level design and balance of mechanics make it so that tiptoeing in and out of shadows is naturally dramatic and of consequence. Moreover, the game has a pretty decent movement system; leaping and climbing are actually really enjoyable, and it makes the more exploration-based levels work.

The other thing I like is a little in spite of itself. We can't pretend that Thief isn't set in a generic world, and that its larger story isn't similarly generic and that its major beats don't really land. But its concept and perspective---its choice of lead character and the spaces it puts them in, maintain interest and provide each level with its own arc. Something as simple as having the objectives change mid-mission based on environmental discovery goes a long way in legitimizing and immersing the player within its scenario.

It's a game where individual chunks of it are exquisite, but the quality of the levels, which I'll add feel very separate from one another, is inconsistent. There is glue holding it all together and that glue is very visible. Sometimes it's visible in its narrative presentation and other times it emerges as mission design that feels contrived (the switches in Undercover, the ghost fetch quest in the otherwise terrific Return to the Cathedral). Thief is an imperfect game with a wonderously imaginative central premise and mechanical execution. I'm looking forward to playing the sequel.

Also a theoretical extra half star for The Dark Project over Gold. Two of the additional levels are the worst in the game and just add bloat.