Halo 2 > Halo 3 > Halo 3 ODST > Halo Reach > Halo CE
Based on campaigns.
Halo 3 is great, but TBH I'm enjoying Reach now. I have to be lucky to find a match in Halo 3, and when i do i am matched up with noobs and derankers.
I love Halo 3, and if more people played it i would too