Hitman World of Assassination! I put off playing it because the purchase model was so fucking confusing, but now that I got it I'm having a blast! These games have some of the best level design I've ever seen, the way IOI integrates story with natural progression through the level is incredible to see. I've never seen a level like Sgail where a player must choose between either climbing the physical structure of the level, or climbing the social ladder through disguises that grant you increasing influence.
I'm on the Chongqing level, and the neon lights look absolutely gorgeous.