one of the most engaging and memorable experiences I ever had on XBL
you could superbounce, dummy, legitimately get outside some maps, sword cancel, etc etc and all while in matchmaking. that was one aspect. it was also one of the best competitive games you could ever hope to play. "Red team wins ties!" was great. being able to talk to the other team in-game was completely different from now, as party chat didn't exist (only 2-person private chat). you could psych out or mislead the other team simply through using your headset. the maps were all great in their own way (even the DLC) and the playlists stayed fresh for well over a year. there was no time limit in the post-game lobby, so you could just sit there and talk trash for literally an hour (done it before). it just seemed like Bungie wasn't as concerned with fixing all of the game's glitches and making sure that every map was air-tight and un-explorable - as they are now. and the game wasn't catering to any type of player, it just existed for our own enjoyment
the only games that can compare for me in terms of the incredible online experience are Rainbow Six 3, Midtown Madness 3, Splinter Cell: Pandora Tomorrow, PGR2, Return to Castle Wolfenstein, and Ghost Recon
Halo 3 was awful imo and Halo Reach is a little bit better. I am sick of the AA though and find myself wishing that Halo 2 could just be remade with all of its faults still intact