I have to agree. I was lucky enough to get Halo 3 before launch day and the excitement of that moment was nearly overwhelming. We were at a conference in Orlando at the Dolphin over at WDW...at the same time, there was a Halo 2 MLG tourney in the basement. We watched Str8 Rippin kick everyone's butt then headed to the room and enjoyed some all-night Halo 3 action. It was great.
However, after completing the game's campaign, and reaching what I thought to be a respectable level in online play, I got bored. The new map packs helped to revive my interest for a time, but not nearly long enough. I too got hooked on COD4, and never turned back.
Honestly, the only time I even put the game in is during game-day here at my office. It's still a great system link game for 12 players. That's something I've always wished Infinity Ward or Treyarch would put in the COD games.
EDIT: Speaking of game day...if you wanna' check out the Halo 3 pics on our 3 Hi-def screens at the office game day event, check this link. Good stuff. http://picasaweb.google.com/lzzrdboy/GameDayEvent#
Anyway, just my two cents.
Peace Out!
The Reverend