Oh, Gears 4 by a parsec.
I adore Gears 4. The campaign is robust, and packed with interesting mechanics, enemies, weather effects, and set pieces. Multiplayer is a joy, thanks to some cool modes like co-op versus. Horde mode is the deepest yet, although diminished somewhat by microtransactions (which, unfortunately, infected Halo 5 too). Plus, many of the modes are available offline with splitscreen and bots.
Halo 5, conversely, is a disappointment. Multiplayer is vastly improved over Halo 4, but it's not enough to overcome what's easily the worst campaign in the series.