Never got to experience Halo CE on big enough LANs. Just on the PC, and it was fun as hell. Played that shit semi-competitively, it how I met my first gaming friends.
But Halo 2 was a force of nature. No other game, not even CoD, has come to dominate its platform as much as Halo 2 has. People would literally sit in Halo 2 lobbies to talk. We had PreGame Lobby custom gametypes, just to have the name. It was the Xbox Dash before the Xbox Dash. EVERYONE played it. The community was so tight then. Remained pretty tight throughout Halo 3 especially with Bungie giving us Forge, Theater, Filesharing. And then sort of faltered with Reach due to Reach not being as interesting. The community, to me at least, is struggling under Halo 4. In part due to the gameplay, but also in part that it launched incomplete.