I'd give it a bit longer, two of my mates were avid halo 3 players and it's taken them ages to get into. Funnily enough everyone I know who played 3 alot have struggled tot get into reach. I love it probably because I hated 3 (FYI I was unstoppable on 2).
Traded it in at asda an got 29 pound today, fed uyp with halos tbh i can play them for a while but the novelty wears of so quickly, might be getting MOH tomorrow though.