I binged my way through the entire collection over the past two weeks. Played every single game on Heroic.
I think I only encountered one crash, and a handful of instances where the game would minimize to desktop, but aside from that it was pretty much a flawless experience.
Ran really well at 1440P / 120FPS on a 1080Ti. For about 70 hours of gameplay that's really not too bad.
The only thing that I really didn't like were some of the artistic choices for Halo CE: Anniversary, they really changed the entire atmosphere of some levels (especially the flood).
Halo 2: Anniversary on the other hand is a fantastic upgrade when compared to the original, and kept the original artistic vision intact.
Shame we didn't get Halo 5 added to the MCC, and having played it recently it's a shame that they pretty much ignore the entirety of Halo 4 (not perfect, but a good starting point for a new trilogy).
As far as I've heard the only real outstanding issues have to do with Co-Op, so one final patch to address that would be nice.