One of my favourite games of the year, not only is it beautifully designed with a fantastic in world experience. It also has a really involving storyline, your decisions also make a real difference, if you go for the stealthy approach you have less guards/rats/weepers and that makes each mission after that so much easier to complete.
The only fault I have with it is how difficult it is to do the stealth approach, you can increase your crossbow arrow supply but not your sleeping darts which does make long distance stealth harder.
Also, word of advice, when trying to do the steath, DO NOT throw unconcious guards over railings down cliffs or stairs. This can kill them and ruin your Clean Hands achievement.