Sunset Overdrive for me.
I still don't know if I want to pick up an Xbox One yet (got my WiiU and PS4), but that title could be a deciding factor for me. I just need to play it a friend's place for a little while before plunking down $560 plus taxes and take the plunge.
It's a shame, too, because the other big release, MCC, doesn't really interest me. I lost a lot of faith in their ability to deliver a good, long-lasting multiplayer experience after Halo 4. That one's definitely going to be a wait and see thing.