I appreciate Halo 5 is a "massive" game for the XO, but, to be honest can't see me picking it up myself, never been a big fan of the series, I have played Halo 1, 2 & 3, had some good times on Halo 2 MP, but, other than that none of the games have been anything
special "to me" the single player story/campaign always bores me to tears.
LostKauz you should have seen Gamescom 2015. There were a lot of exclusives. There is a lot more than Halo and Gears. Besides, why not keep making games if people want them? Sony does the same with Uncharted, God of War, Killzone, Little Big Planet 3 and
so on and so forth. They rely on many sequels of the same few games just like MS and Nintendo do.
Here are a few X1 exclusives I can think off the top of my head. Regardless if they are also for PC or not doesn't matter as they're not available on a different console.
Cuphead. Below. Inside. Crackdown 3. Scalebound. Quantum Break. Fable. Forza 6. Recore. Ashen. Gigantic and Sea of Thieves.