What's wrong with Halo 4?
Single player:
- New enemy designs borked (extremely annoying to fight, uniform color scheme makes it hard to tell apart classes and identify which weapon is about to kill you)
- Small linear environments
- Essential story info shoveled into short videos that are only available on Xbox Live's Halo media hub, Waypoint (maybe also through the site, but I haven't checked)
- Weapons on the ground despawn as soon as you leave the area (sometimes before)
- No more theater for single player modes
Multiplayer:
- Comprehensively COD-ified. Reach ruined the defining characteristic of Halo's multiplayer: everyone starts out on a level playing field with the same weapons and abilities. Halo 4 takes everything Reach did wrong even further, and adds perks and weapon drops on top of it
- Weapons spawn in random locations
- New weapons too samey—everything's just a variation of existing types
There's more but I think this is a decent summary. Note that a big patch came out for matchmaking that I haven't played yet. It might have solved some of the game's original issues.