It's no Dishonored.
I don't hate Thief. Let's get that right out of the way. But it's such a weird game for being a seemingly straight forward AAA title.
I feel like Thief would've been a better game if Dishonored didn't exist. Not just that Dishonored is better by comparison (because it is), but it feels like Thief and Dishonored had a lot of parallel construction. Once Dishonored was released, well before Thief, it's like the developers just gave up.
The levels are pretty linear, particularly when I got to the end of the game. At first I spent a lot of time searching around and trying to get all of the loot from each level, but halfway through I realized that I didn't need all of the cash. Thief gives as much as you put into it. If you want to crawl around in the dark and pick every pocket and memorize guard paths, there's plenty of it to do. I didn't find it all that compelling though. When I stopped creeping around, the game didn't put up much resistance preventing me from making a beeline to objective markers.
It does do a lot of neat stuff like animating Garrett's hands as he picks up loot and pops open safes. I like those little touches. It's also a dreary and bleak, but well-detailed world. There are a lot of notes and journals to collect, but the fiction isn't particularly interesting. It has two boss fights, which don't necessarily require turning them into pincushions but they still stand out as strangely out of place. Again, a weird experience.