Sea World gets packed too; but different than Disney, because you don't have to wait in very many lines. Food and drink stands seem to be the only lines except for the 3 rides.
We went Memorial Day which was busy and decided Arctic Adventure was not nearly as enjoyable because we opted to not do the ride and walked through. The crowds at the windows to see the animals were just too huge to even spend time watching the bear etc.
Fireworks would make putting up with the crowds on the 4th worth going though.