Even without going on the coasters, I think there is plenty there that an 11 year old would love, especially if he is a Harry Potter fan. There are a lot of fun rides based on superheroes and characters that your son most likely knows (like Spiderman, the Transformers, and the Simpsons). You will find plenty to do.
I think it's worth staying at one of the Universal resorts that offers the Front of the Line access (Portofino Bay, Hard Rock, or Royal Pacific). It's great to be able to go through the express pass line and get on the rides without a long wait (I think the most I've ever waited in line using the express pass was 15 minutes, but usually it's just a few). You also get to enter the Harry Potter area an hour early (this perk is also available with a stay at Cabana Bay).