You can bet this is the response I hear most about IOA more than any other.
My son and I had a pact that we would not get on the roller coasters at IOA until he was tall enough. That was back when it opened in 1999. We'd gone back 10 times before he was tall enough in May of 2001 and it's STILL his favorite park in Orlando. I was the moderator of this board before I had even been on the Hulk!
What I'm trying to say is that the Islands of Adventure offer so much more. The theming, the sights, the sounds, it's an experience in itself! The coasters are the famous things, but it's like basing Magic Kingdom on the "mountain" rides!