I have been playing the game since it unlocked on Steam and I have to say the game has really surprised me so far. It looks absolutely outstanding for one thing. The lighting, shadows, particles, reflections, parallax occlusion, tesselation and other graphical elements all add up to one beautiful game. I also love the art direction.
What's more surprising, however, is that it runs extremely well. I am maxing it out, aside from SSAA, and getting a solid 60fps. I only have an HD 7950 and i5 2500k and I truly didn't expect to get such good performance in this game. I can honestly say that the ratio of this game's performance to how amazing it looks is by far the best I have ever come across.
Part of the reason for it's great performance is that the devs actually properly multi-threaded the engine. pcgameshardware.de did some benchmarks and found fantastic multi-thread scaling. Read about it here: http://www.pcgameshardware.de/Thief-4-PC-98521/Specials/Thief-Grafikarten-und-Prozessor-Benchmarks-Mit-dieser-Hardware-gehen-Sie-ohne-Ruckler-auf-Diebestour-1110793/
Unfortunately, however, the game doesn't run so well on the PS4 and XB1. This is not just unfortunate for the gamers that play the game on those consoles, but also for the game and developers of the game themselves. I truly believe that part of the reason for the mediocre scores from a lot of reviewers is the poor performance of the versions they played. Choppy framerate really does drag a gaming experience down. It even gives you a more negative impression of a game's visuals than you otherwise would have. I was expecting to see this game get scores mostly around 8/10 and I think the reason we are seeing an average closer to 7/10 is due to the choppy experience it offers on the consoles.