Purely subjective and purely personal, but I consider Halo 2's to be the worst. The excitement on release day of a new Halo game, my mind reeling with the prospect of multiplayer online, just to find it waa battle rifles pretty much 24/7. I spent a week or so struggling to love it before never touching it again. I know most people consider it to be the best, but I ain't on board.
CE and 5 are the most enjoyable.
CE and 5 are the most enjoyable.