Halo was a lot of fun co-op on Legendary. It made the game for me. Multiplayer was fairly fun (but not spectacular) fun, especially when doing Warthog tricks. There were some really cool moments in the campaign, but also some kinda lame ones (the Library with Guilty Spark got incredibly tedious and annoying). Overall though, I found it to be a lot of fun though.
Halo 2 was alright, but they blew so much potential. After the first trailer when it looked like Earth was under attack and then come to find out its just one city. The Arbiter levels kinda sucked in my opinion, and then out of nowhere they pull that giant plant thing and its just kinda like WTF is going on anymore. It was ok, and had some brilliant parts, but as a whole is fairly forgettable. I did like some of the imagery, but I think they would've been better off not spending so much time overhauling the graphics (which at times looked gorgeous and other times could look horrendous) and focus more on the story/gameplay.