Well I like being part of a vibrant and growing community.
Having a community actually GROW in a game is incredibly rare. Pretty much reserved for a select few PC games.
I'm with you on the vibrant part though. I think a big reason why the halo community feels lackluster to me is that 343 did launch with a limited multiplayer experience.
I'm really thankful they got the core gameplay down. It's one of the best in the series. But they messed up pretty big by having a really barebones feature set. Halo CE had more gametypes.
What's worrying, and I hope they announce something soon, is that there has been NO WORD on old (or new) gametypes coming back. NO WORD on more customs customization. NO WORD on what the filebrowser will be like or if its even coming (just a screenshot of an old build).
Infection has become a casual Halo staple and a building block for interesting custom mini games. 343 killed its functionality in Halo 4 and now they didn't bring it back. Grifball, an entire community, is essentially dead with no assault gametype. Don't even know if hammers are in the game.
VIP, Territories (maybe strongholds can be modified idk) KOTH, all these game modes had interesting functionality that let really creative people make really interesting games out of them.
Halo 3 MM was a lot of fun, but some of my most fun in Halo 2 and Halo 3 was in customs.