Currently Online 
Having played all 5 games I can say that I eaily found Halo 3 the most fun, mainly as it is the only one I played online with my friends (I didnt have live during Halo 2's era). In reflection, I think Halo 2 had the most well developed plot of the 3 games, although ODSTs was better that Halo 3's.
ODST was more interesting as the battle style was a bit different to the trilogy as you dont play as a Spartan. Firefight was good and Im really hoping it returns in Halo Reach with the ability to do matchmaking.
Wars was fun though I eventually got frustrated with the multiplayer. It allowed me to play Halo in a way that I had thought would make the battle seem more real and massive, but if they ever make a sequel I think theres a lot that can be improved on. Im hoping some of The new vehicles from this game, such as the Cobra and the Locust make an appearance in Reach, as I think they could help define the atmosphere of the game.
