Definitely Shadow Order
I second this. My biggest win this year and my biggest multiplier (I think) plus a folder full of Shadow Order screenshots. Its also a little different.
I like Razor Shark also (my second biggest multiplier (I think)) but agree its a dangerous game.
Honourable mention to Carnival Queen - would have walked it if I could see the potential coming in.
4 Edits later - DOA2 without a date should lead and others should follow. Clearly living up to its advertised potential. Well done Netent!