Our first trip to UO was when DS was 6.5 and he LOVED it. No one went on the huge coasters, and he and DH didn't go on Forbidden Journey either, but we all still loved it. DS loved being in Wizarding World so very much, and he took full advantage of our hotel express pass and the ability to go on things by himself. (at UO if you're 48" and meet the height of the particular ride you can go by yourself) Well, I went on Hippogriff 14 times in a row with him. On the last ride I saw the sign about 48" (the actual height for Hippogriff is 36"). Later in the day when he wanted to ride the Nuthouse Coaster 15 times, he went alone. I sat on a bench.
We went the second and third times when he was 7, he rode Forbidden Journey that time and loved it. Well, not the "acromantulas", but I don't love them either. I'm the only one in the family who has been on BIG rides so far, like Dragon Challenge and even The Mummy, but they found other things to do and had great fun there. ETA, not true! DS insisted that we go on Rip Ride Rockit, so we went. EEK! Now he's tall enough for *everything* and so I'll get to experience it all, too. (no way I can let him go alone on the big rides, that's a scarier idea than the idea of me riding them!)
We loved UO! It also allows you to have the homework of watching all sorts of new movies.

We watched Men In Black and ET before the first visit. DS hasn't seen The Simpsons but still loves the ride. If you're going after Transformers is open and they've seen it, I bet they'll like that. And we are beyond excited for the Despicable Me ride. We went on it when it was Jimmy Neutron and that was great (even though we had never watched that show), so to have the attraction themed to something we love will be great! Oh and Shrek 4D is *hilarious*, in our opinion.