Great America has been one of the best theme parks I've visited. I grew up with Great America out here in the bay area, and I know that the park attracts visitors from all over the country.
If you've never been, you should check out the 70+ rides and attractions they have. I've been to shows here, and I always have a good time. If rides aren't your cup of tea, some of my friends come out for shows and to have a picnic, or to hang out at the water rides/slides. You can even check out Planet Snoopy. It's a good time for the family and kids.