My 4-year-old son loved Universal last October. Loved, loved, loved it.
That being said, with his thick-soled shoes on, he was 42 inches. So we were able to do the Popeye water ride, the Jurassic Park ride, Men in Black, rides like that with a 42-inch requirement.
Rides we went on included: Despicable Me, Transformers, Spiderman, Shrek, Men In Black, Popeye, Jurassic Park, Dr. Seuss, Flight of the Hippogriff, Simpsons.
He wasn't able to do Dudley Do-Right's Ripsaw Falls, but we're headed back in November when he's 5 and he'll be able to reach the 44-inch requirement then.
He's also a huge superhero fan, so we did the meet and greet with Spider-man, Captain America, Wolverine and Cyclops.
Also, Gringotts is 42 inches. So he'll get to experience that for the first time. Lots to do for a 4-year-old, especially if they're 42 inches.[/QU
I agree with the above! My daughter absolutely loves Universal! We have been going since she was 3. She just turned 5 on our last trip in August and is finally 42". She loves the coasters she can do and all the other rides she is tall enough for.