Gears 4, somewhat unexpectedly.
I replayed Gears 3 with a friend, and that's still a bit of a bummer, but then we started Judgement, which neither of us had played, and the level design of that really reminded us of how great a Gears of War game can feel.
The control mapping shakeup I'm not a fan of at all (especially how you're expected to roadie run with A and swap weapons with Y - it's like they sporadically didn't get fundamental things about Gears), and the tower defensy Horde mode stuff I would rather they keep far away from the campaign, but other than that it really makes me confident that Gears can deliver in spades in terms of (at this point) old school and pleasantly to-the-point cover shooter thrills.
Setting it 25 years later lets them add some more nuance to the backdrop and story, and you can even tell from Judgement that the writing has inched north of the "bitch" this and constant, grating meathead quips that of the prior games.
So yeah.. Bizarrely enough that's probably the one. I mean I'll like other games more, because I always do like brand new games more than something I pretty much know what to expect from. But that's... per definition not something I can anticipate.