I wouldnt recommend this game. I love stealth games and I really wanted to like this game, but I just couldn't/ As other people have already covered the mechanics are decent but the level design is very linear and consequently doesn't provide much of a challenge and isnt rewarding to crack. Go play thief or hitman instead.
The game is superb, with excellent puzzle platforming, art design, music etc, the only thing holding it back is it's poor combat which is unfortunately very present. Compared to the good here though any set-backs are incredibly minor. I would thoroulghy reccomend this game top everyone.