I got back home from my trip today. We did 4 days at dizney and 1 at IOA. We stayed on site to get into Harry Potter world early and to skip the lines.
1. Do you like reliable crowd calendars? The only one I am aware of is
undercover tourist. Yesterday (Thursday 11/29) was a yellow, use caution kind of day. Apparently that means no lines anywhere in the park over 10 min. Empty seats on the dragon racers. So yeah, the crowd calendar isn't so good. Obviously not Universals problem, but the reliable outside research just isn't there. (Anyone else want to pitch in here?)
2. The big fancy harry potter ride is awesome. BUT it's an awesome motion simulator. Those type of rides wreck me. If you have similar concerns consider: one of the super headliners is out of bounds and one of the major reasons to stay on site (getting onto that ride before the crowd) is a moot point.
3. The Marvel characters are not as well costumed or as good as match to the template as WDW. At both parks there are iconic characters (Mickey and Spiderman) and less iconic the (kid from up and Woody Woodpecker). [Find me 50 kids under 14 familiar with woody woodpecker and I will change this line]
4. The roller coasters are awesome. If your party is tall enough it's a good time. (not as good as Cedar Point, but better than most of WDW)
5. Butterbeer is Yummy. Pumpkin Juice is not.
6. If you want to have a youngin do the wand thing Olavanders is awesome!! We stayed on site, immediately got into line for Olavanders, my kid was first in the shop for the day and was duly chosen. He has read the books and was psyched. If you do not intend to buy a wand or are a muggle skip Olavanders.
7. If you have food allergies U.S. isn't even in the same ballpark as WDW. I mean not even close. NOPE NOPE NOPE. The head cook at one place came out to talk to my wife about her gluten allergy. That's good right? He recommended the normal Spaghetti. Epic Fail. There are three safe places to eat at IOA. Two sit down and a counter service kind of place (so I'm told, we didn't go to them). It's a small park so maybe not a huge inconvenience, but not nearly as good as WDW.
8. As someone else mentioned Theme. The staff in Harry potter world didn't really carry through on the theme. The details of the buildings are cool. The pre ride area for the ultimate harry potter ride is worth getting in line for, but then the staff just doesn't carry through. I noticed and it did detract from the experience.
9. On the other threads you will hear folks who drink too much Disney kool-aid talk about Magic. Magic is just a well executed customer service strategy; however, they execute that strategy really well. In my - limited - experience the difference is noticeable.
With all that said, wait for the 8yr old to grow a bit taller then go. The best part of the park (again note I only went to Island of Adventure) is the thrill rides. Your girl is too short for the best part.