If you want to bypass the web, check out Whiteboard, although not a game, uses a device's wifi connection to collaborate in realtime, with very low latency. I think that if you can figure out how to make your game connect to another's device like that, you could pull off some quality gaming ideas.
At least, that's one of the things I want to do.
If you need to game over the web, you're not going to easily get around the problems @John Douthat mentioned above. For games like Go (see Tetsuki for an example) and Chess, that's not a problem, but a shooter (obv) would be. 
And, no, I have no affiliation with Whiteboard (or Tetsuki for that matter), I just think the tech  is cool.