This is a good game. Before you buy it: be aware this is a pure stealth game, from it's core to it's every element (maybe combined with a little RPG), so don't go out and buy it and then complain about how there is no combat or enough action for you. BUT if you like stealth, avoiding combat, and like to go around things, looting than this is the game for you.
Those guys at Eidos made a great job. Everything looks beautiful and detailed, although the great graphics come with a price. There are loading screens between city districts, but it is worth the wait. I have never seen so realistic and detailed environment (only in HD modded Skyrim). The player has lenty of choices how to complete the goals, and has many tools which can be useful for obtaining the collectabl items.
The gameplay is great, graphics great, story is fair all in all it's a good game.