the halo series deserves the critical acclaim it got imo. To me its up there with metroid and zelda as my favorite franchises that i can almost always rely on not regretting purchasing the newest game.
My ratings
Halo 1 (92%) Awesome campaign but not much replayability
Halo 2 (90%) Purely because at the time it had the funnest online of any console fps period. Campaign was good for the first two levels, and then got annoying.
Halo 3 (98%) Forge alone has made this game have unlimited re playability for me. Campaign was great since i could easily play it co op online. Multiplayer was a blast. Custom games is what made it better then every other online game I've played though.
Halo Wars(80%) By far the best console rts I've played but to be honest it would have been twice as fun with a mouse and keyboard. You just can't play rts's with a controller unless they are greatly dumbed down or it gets too hard to manage.
Halo 3 ODST(85%) Great campaign, firefight's awsome. I would rate it 90% if i had bought it for $35 but my halo 3 disk was broken so i got it week 1, because the game felt like a big expansion so $60 was steep.