Your site appearance should have a lot to do with your goals and the audience you're trying to reach. If you're keeping it simple, then your site has achieved that goal. It does look a little plain, but again, if you're not trying to be artistic and simply convey information, then the appearance shouldn't be an issue. I'm not a fan of the advertising, but I understand that it can be necessary.
In terms of improvement, I think that there are no obvious navigation clues other than menu at top. And there isn't one particular item that stands out as your primary subject.
I hope that helps to provide some feedback for you!