Some thoughts:
-Looking at Obsidian Portal for the first time in years, I found a bunch of campaigns near me... last updated 5+ years ago. "Undead" games will probably be an issue for your service as well. Perhaps you could add an additional filter field for recently active/updated games.
-Following the last point, some groups might be "passively open": meeting regularly IRL, but not active on Roleplayful if there's nothing to update.
-I live in Chicago. It might be useful to have something that'd allow people to put in location tags for, say, the north side and nearby suburbs. Somebody in the city using public transit could take an hour or more to go to the other side of the city.
-It might also be cool if I could list more than one system if you're open to different options, but I can think of some arguments against this.
Thanks again! The best group I ever had (spanning ~4 years) was started with a notecard thumbtacked to a bulletin board in the back of the game shop. I try to keep an eye out for newer digital options!