I wasn't much of a Halo fan at the beginning of this gen. I bought MCC and played some Halo 4 and CE but meh. Then I bought Halo 5 and loved it even though I had no idea what's going on with the story. Went back to MCC and started playing those and I've now completed all those campaigns + ODST many times :P There's some magic about those games, they're fun to play over and over again and I love it there's so many achievements to unlock in MCC.
I started playing MCC again recently because a friend of mine bought X1X. We played through Halo 4 on heroic the other night and it was a blast. I also got addicted to SWAT playlist I never even tried before.