I mentioned Basis too!
There are probably more but I can't think of them at the moment. Mostly talking about the Team Slayer task anyway.
I really think there should only be a handful of Forge maps in matchmaking as 99% just isn't good enough. They're fun to play in customs every now and then but that's about it. And because there's a rarely a really good map made in Forge I also think there should only be 1 or 2 Forge maps in each playlist. If there would only be so few Forge maps in MM people would probably also complain less about all of them looking grey and similar to each other.
Just looking at the amount of Forge maps in Team Slayer makes me disgusted, and I say that as someone who Forges regularly. 19 Forge maps and only 6 on-disc non-DLC maps? That's crazy. I'd rather have a few good maps that a shitload of terrible and mediocre maps (like is the case right now).
Well, the original plan was to have separate community lists that acted as mass beta tests (hence Community Slayer and Community BTB only being around for a week), then the most popular maps in voting would get one more pass from the author and pushed to the rest of matchmaking.
The playlist cap and the Anni split redundancy have pretty much killed the chance (in my opinion) of seeing special lists like Flagstravaganza, Community Slayer / BTB, and so on come back. Some time ago they said the TU Beta list was coming back, but I have no idea what the TU Beta lists would even be used for this time around with Halo 4 breathing down Reach's neck.
The only lists the CCs can push to are existing ones, and therein lies the minefield of opinions on maps.