Island of Adventures is the second Universal park (It's full name is Universal Studios: Island of Adventures). It's where Harry Potter is (not in Universal Studios). They're right next to each other.
Compared to Disney, US and US:IOA are...underwhelming. My husband and I had fun, but, eh. It's not a MUST DO (and we made a whole trip there because I'm a HUGE HP nerd). I do love IOA for some stuff. They've got a whole section for Superheroes, which has a hulk themed rollercoaster, a Spidey interactive/3D type ride (dunno how to explain it. It's pretty neat) and a couple little carnival type Xmen themed rides. I think the tower drop is Dr. Doom. When we were there, Capt. America, Cyclops and some Xmen women were making appearances. =D IOA also has Seussland, which is ADORABLE, Comicbook/cartoon area (old ones, like Dudely Do Right, Popeye, Marmaduke, Betty Boop, etc), a Mythical/Fantastical section, and they have the Jurassic Park area. Of the two, IOA is by far my favorite of the two parks. US is dedicated to their movies,s o they've got Simpsons, Men in black, a beetle juice show, random hollywood stuff (they have a special effects/make up show that was pretty neat).
If you're interested, I can message you links to my FB albums of the last trip my husband and I took and you can see pics?
I don't remember if you've settled on a date yet, but the one thing we hated about US/IOA was that their queue lines are AWFUL. We went in late July, and the sun was brutal, the humidity was horrific and there were no shades in the lines, most of them were outside with no shelter. I haven't been to Disney in the summertime, but I really don't remember their lines being that un-sheltered.