Tommy’s list is pretty good as a rough guideline. I’d move a couple things around, but… that’s more or less a good list. So I’ll just throw some general thoughts and opinions on top of it…
I’ve been to Universal/IoA dozens upon dozens of times, and have done every ride, show or attraction there at least once… except for A Day in the Park with Barney (And it’s honestly been on my to-do list for like 10 years, but always gets cut, haha)
There’s nothing there I’d say NOT to do, and I think with 2.5 days… you have plenty of time to do most, if not all of it. BUT… if you have lots of dilly in your dally, I could easily see where you might miss some stuff, so… random tidbits…
Don’t skip Spider-Man. A lot of people seem to do that. Don’t do that. Ride it. If you enjoy it, ride Transformers, because it’s basically the same ride with a change of theming.
The Seuss rides can actually be fairly entertaining if you have little ones, even as an adult. But can also easily be skipped. I’d give them a once over if you have time, but don’t feel bad if you don’t. The kidzone rides all pretty much suck and I never ride any of them anymore.
If you’re not a fan of getting drenched, don’t ride ANYTHING in Toon Lagoon. You WILL come off both Ripsaw Falls and Bilgerat Barges drenched from head to toe. I often skip them for that reason alone. (By the same token, Jurassic Park River Adventure will give you a decent splash, but won’t soak you to the bone. You might come off with a large wet spot somewhere on your person, but you’ll usually drip dry in an hour or so.)
Shrek & Terminator 2 take a lot of crap, because they’re pretty run of the mill 3D shows, and they lose a lot of their luster on repeat viewings… but if you enjoy either movie, they’re worth doing at least once. They’re both mini-sequels to the movies they’re based on.
Poseidon has some neat effects, but it is very cold, and involves a lot of time on your feet. Again, worth doing once… but probably something that could be cut if you don’t have time, as others suggest.
As was mentioned Storm is just teacups. It’s only worth doing if someone in your group is a major X-Men fan. And even then, only barely.
A Word on Shows: See the Horror Make-up Show. Again, like Spider-Man, a lot of people pass this up because it doesn’t look like much from the outside, but it’s basically the best show in the park. Well worth seeing. Sinbad is a decent stunt show, but feels a bit dated these days (but if it’s new to you it could be good?). I’d personally skip Fear Factor (if it’s even open, because it seems to be shut down half the year anyway). I’m not sure if the Animal Actors show is even still running, but that’s skippable too. Cute animal stunts… but… nothing to write home about.