I have been a Thief fan since the first one, I have played the others the moment they hits the shelves but this one held back because of all of the middling reviews but when I saw it on sale I simply could not pass it up. Really for the first time in a while the reviews nailed this on the head overall, both the critical reviews and the user reviews. What is does well it does really well, sneaking around is a blast, finding the unique way into a location is fun, locating that special loot is great, the atmosphere works for me as well, a world between the real and fantastical, between the mechanical and the magical but then just as it hits a groove something reminds you of all the reasons you just want to finish it. The AI by and large are dumb as rocks, I had issues with loading the game where it would crash, causing me to shut down steam and sometimes the PC before I could start it again but the biggest issue was the lack of danger overall. My memory, and it can be faulty, was that the 1st 2 Thief's when you were looting a place there was danger, you felt that at any moment a guard or townfolk could walk in a room, around a corner and catch you red handed but this time around for the vast majority of the time you feel like you are by yourself and if you wanted you could stand up and be a one man band while robbing a location blind and never need to worry about anyone trying to stop you. I have 2 final complaints, 1 - The City I loved all of the nooks and crannies but as the game progressed navigating became a real chore when it should have gotten easier and 2 - End Game all I can say is WTF.
So in summary, if you liked the other Thief games, Splinter Cell and Dishonored (specifically Dishonored and it is so close in tone and feel) then for the sale price this is worth a try, you get 20 or so hours of play and more than half is good to great and the rest like watching a sequel that is far inferior to the original but just good enough to get through.