One of the biggest problems CEA had was the graphics engine. The texture pop-in was absolutely horrible, and i really hope they rectify this in MCC. (also animations and hitbox fixes would be nice)
That’s not an engine problem, that’s an Xbox 360 problem.
CEA ran two engines simultaneously; the original Combat Evolved engine and one that ran the new graphics.
Your Xbox 360 uses 512MB of RAM (roughly 1/2 a gigabyte) which is directly responsible for speed. The Xbox One has not only 8GB of RAM (16X that of the 360) but it’s better quality, so these issues should no longer be a problem just due to the power of the new console. The graphics switch should be near instantaneous, texture-popping shouldn’t exist, none of the problems with lag or choppy frame rate when too many Flood are about or any of that, just by default. They shouldn’t have to change anything, just the up-res to 1080p and 60fps.
As for hitboxes, I may be wrong, but I think they’re the original boxes, but some of the new models are larger, which makes for iffy sniping. Hopefully they tweak that. The animations? That’s probably not high on their list of things to do to get this game ready, but it would be nice.