If you care mostly about the coaster/ thrill rides, then your ficus ought to be the following:
USF:
Tier One Rides (MUST DO):
Rip Ride Rockit
Revenge of the Mummy
Transformers 3D
Tier Two (WORTH DOING):
Simpsons Ride
Escape from Gringotts*
Despicable Me**
Men in Black**
*Considering this is the big new ride, many would disagree with me here. But the simple fact is, the ride is a very slow and basic coaster with continual stops and movie scenes in between. Great for potter fans, but it seriously does not have a lot to offer - ESPECIALLY when you take into account how long it takes to ride and it's proclivity for breaking down. It's an alright ride and all, but it's not worth riding this and missing out on 2 or 3 other great rides.
**Both of these are fun rides, especially if you like the franchise. But may be difficult to fit into your schedule, so they should be the first you cut if behind on time.
Twister, Disaster, and Terminator are all decent if not dated - but on your schedule, these take up a lot of time and aren't "thrilling" at all.
IOA:
Tier One:
Hulk
Dueling Dragons (which is actually 2 coasters)
Forbidden Journey (a lot more thrilling than you would expect)
Spider-Man
Tier Two:
Fearfall (this is a tier one if you haven't been on a drop ride before)
Jurassic Park River Adventure
Skip Bilge Rats Barge and Ripsaw Falls unless you are entirely comfortable getting soaked.
So yea, you can hot all the Tier Ones in a single day. If you want to hit the tier 2's as well, you may need an express pass. If you want to check out the shops and more detailed features of places like Diagon Alley/Hogsmeade and such, then an express pass also helps.
There is a TON to see an do at universal. The first time I went I missed half the rides because I was too busy just going to the rides that stood out to me and seemed like obvious winners. I just got back from a week there, staying on site. That was the 4th time I've been there, and that was the first time I felt like I had actually seen it all.
From a thrill ride perspective though, Rip Ride Rockit is an amazing experience.