I could not agree more!
1. Much longer campaign
2. loads of weapons (old and new)
3. lots of maps, more adventurous and majestic
4. FIREFIGHT!!!
5. UNSC scarab equivilant (not mammoth), and scarab
6. Arbiter (obviously)
7. warrior servants
8. EPIC foreruner vehicles
9. Spartan ops
10. Lots more insight in the campaign regarding the ancient galaxy (precursors)