Yeah, it's fun, but not that much variety. There's around 3-5 different gametypes (depending on if CTF and Headquarters is in the final game) and you can't customise those at all. I Halo 2 you had around seven gametypes, and a huge number of different variants (CTF, 1 Flag CTF, Neutral Flag etc) and you can customise any way you want. Let the flag carrier be invisible, run really fast, run really slow, be able to drive vehicles and so on.
The variety in gametypes and the customisation was what kept me playing Halo 2 multiplayer so long. And now Halo 3 is looking to have even more customisation options, gravity, player speed and all that jazz. And with Forge, Saved Films, online co-op, campaign scoring it's just mind blowing how much there is to do..