Pros:
New weapons (BR/DMR is also great)
Cons:
Forge is terrible
Removed more game types than added (assault, juggernaut, race, headhunter, stockpile, invasion, territories)
No weapons on maps
Custom games lack customization (flood especially, not as customizable as infection)
Instant respawn annoying (especially in certain game types)
I sat here for a full 10 minutes trying to think of something that was a direct improvement over Reach/H3 for the pros, and I was disappointed to only find 1. :/