Maybe, but I never had the same 'WOW!' experience with the later games that I had with Halo 1. Which was the game that made me buy an Xbox 1, I played Halo 1 on a sunday with Denny my partner and bought an Xbox the next monday ;-)
Halo 3 is great, we played all three parts in coop mode and, in addition, I played Halo 1 and 2 in single player.
I also enjoy the online multiplayer, but I have one minor compaint here: the online ranking system is somewhat intransparent compared to Call of Duty 4, for example. I was working on my promotion to Lieutenant in Halo 3 since game release, never knowing how to get these experience points besides winning a match (and I just discovered you GET experience points for matches even if you don't win). In CoD4, you always see how many points you earn and you know when you will be promoted. In Halo 3, sometimes your experience level will rise, sometimes it drops - even without leaving a match or killing a team mate in friendly fire. Today, I finally managed to get my promotion - I was promoted to Lieutenant after playing a Lone Wolves game in which I didn't even win. Maybe one of you other Halo 3 players has some inside into the ranking system? Any enlightenment would be appreciated ;)
Besides this, I agree with you: Halo 3 is the best part of the series, closely followed by Halo 1 which was my personal XBox 1 system seller. I was totally overwhelmed then, it was something new and the graphics were revolutionary. Halo 2 was somewhat disappointing, it ended too abruptely and wasn't very innovative. It got the impression it was more of a Halo 1.5.
I'm a big Halo 3 buff. A friend (Marine JAG working on appellate cases) and I frequently play as a team, but we have been searching high and low for others to form a larger team to play with. If anyone is interested in playing with a couple of older, dedicated players who are more interested in cooperation and small-unit tactics than pwnage, feel free to send a message to my gamertag, Mithradates23.