So the biggest thing I can see is the ability to sort and filter what's on the homepage. Judging by what's on there now, the new games aren't very popular. Instead of focusing the bulk of the space on the new, untested games, perhaps show the popular games. Its likely that people will prefer them.
For possible add positions, you might try: inline with the games, as one of the headlining photos, alongside (vertical) the game while people are playing, or the company mochiads.com.
On the playing game view, move the other games to be alongside the game. That might make it more impulsive to click on to another game, rather than having to scroll.
The pagination on the game list page (#3) needs more spacing on the top. I'd like to see more sorting here. Specifically, sort by # of plays, sort by average rating, most comments, etc.
The search page looks completely unformatted. It might be worth tiling the results like the rest of the site, or at least experimenting with that. It also looks like you have duplicates, so that should be looked into (Doodle God, specifically).