... describe what you wish an RPG did for you which no RPG currently does to your satisfaction. You get to name just one thing, one sentence.
Difficulty: you cannot name or reference an existing RPG. It's not the "I like the way X handles Z" promotional thread, it's the "I wish Z was handled better, but I haven't seen it yet" thread.
Disclaimer: I'm not nearly as prolific a gamer as I could be, so it's highly possible that I just haven't found my wish yet.
I wish a free bazaar existed for community submissions to a universal game system, that would have not only an endless selection of free house rules, characters, maps, adventures, and gear, but it would also have a rating system that would allow you to get an idea of the quality of a submission before you downloaded it (and made your game group suffer through it that evening).
Sentence two: It would also have a nice search function to allow you to quickly sort through the mountains of community submissions.
It's a little meta-game, I know. But there's no reason why I can't go to, say, "CommunityRPGVault.com" and do a search for "D&D 3.5, vampire adventure, level 5" and get something remotely relevant and playable.