There are defninitely other things to do. A fair number of them are simulator rides, which I mention because I have a family member who won't ride simulators or coasters, and they have a harder time enjoying the Universal parks. Not that there aren't still SOME things to do, but it definitely subtracts drastically.
NON-Coaster rides at IOA
Forbidden Journeys (simulator)
Doom Tower (drop tower)
Popeyes Bilge barges (water ride)
Dudley (water ride)
(I think one more water ride in cartoon lagoon)
Jurassic Park river adventure (water ride)
teacup style ride in Super Hero Island (can't think of it's name)
Cat in the Hat
High in the Sky train
Seussical carousel
Red Fish, Blue Fish
SpiderMan (simulator)
I am probably missing something, but can't think of what it is right now.
NON Coasters IN USF
Despicable ME (simulator)
Shrek (show/simulator)
ET
Simpsons (simulator)
Transformers (simulator)
Men In Black (shooting game/ride)
Disaster (ride/show)
Twister (walkthru show)
Again I am probably missing something but that's the majority not including straight shows.