Hardly a deal-breaker, but if you redesign at some point I'd consider making the navigation smaller so people don't have to scroll to play games if they have 800px vertical resolution (such as on a typical 13" laptop).
Your images don't display under "link to us", you might want to fix that.
I think there's a bit too much on the front page - if I were you I'd consider dropping the tabs near the bottom, which seem largely unnecessary to me.
Perhaps you could also offer points for referrals to try and make it go viral? Although, admittedly, it might encourage people to abuse the system.
Edit: One more minor thing, your "More Features" link is a little ugly and doesn't match the rest of the site, and clicking the clicking "Sign up" and "View Prizes" in the pop-up doesn't work correctly.