Having put 90 hours into Skyrim, I'll nominate Portal 2. Skyrim has it's charms, but they ceased to work on me after about the 50th hour and the rewards started to be outwieghed by the time required to achieve them. Portal 2 on the other hand was an excellent narrative, laugh out loud funny at times and introduced some excellent new mechanics to keep its gameplay fresh. Kudos also to Arkham City- although not as compelling as it's predecessor, I'm still finding things I haven't seen before and it's still fun to play.