I have played Halo 1 and 2 (don't have an XBox anymore to play 3), yes i enjoyed the game and multiplayer was OK but once is enough. It had great SP elements and I was happy with the the two weapon limit, especially when in Halo 2 you could hold two at a time, but really, halo lacks Long-Term playability. Once you've finished it the story is boring to play again and all you have is un-inspiring multiplayer, the only fun thing about multiplayer was the vehicles (used to blow my brother up with the scorpion when he was in a banshee. Ahh, good times
). Half-Life really does conquer both Halo1 and 2 mainly because of the custom mapping ability and large fan base. Honestly, if Half-Life 3 could provide an array of good vehicles, a wide range of effects, tools, good storyline and monsters, and all easy for mappers to use or modify then Half-Life would reign supreme over all other games. That is what I think anyway.