Can you really have that though? People would just make offensive room titles or play unfun uncommon gametypes.
I think that if it is organized by gametype and author, it would be reasonably easy to find a custom game you are looking for.
And it wouldn't be too unreasonable to assume there would be an option to report someone for offensive content.
Then simply ban that person from showing up in the browser for a period of time.
Having categories like "most played gametypes" or "gametype of the week" would be cool too.
On that note, it would be really nice if gametypes could be linked to specific map variants as well.
That would help with keeping a predictable, player ran, custom game environment.