First before giving my synopsis and comparisons, I want to state that I am a DVC member and love wdw and have been going to WDW ever since I can remember. It should be known that US/IOA and is MUCH different then WDW and is mostly geared towards a teen and adult audience where as most of the attractions at wdw are geared towards all ages family experience. As others have noted US/IOA has a lot of thrill rides but also has many "all ages" rides as well. A couple of other things worth noting, IMO, are that the price differences are drastic (gate, food, alcohol, resorts, etc) and the access and size of the campus are drastically different. Op (or anyone else) - if you have any additional questions and or want additional information/explanation after reading this short novel of mine, feel free to ask (or to send me a PM) as I frequent both resorts and have done so with a wide range of ages in my group(s) when visiting Orlando. With those things being said, here are my opinions...
Universal IOA Attractions
The Amazing Adventures of Spider-Man® - WDW, Dinosaur with 3D experience without the fright factor
Incredible Hulk Coaster® - WDW, Closest would be RNR Coaster
Doctor Doom's Fearfall® - WDW has nothing like it
Storm Force Accelatron® - WDW has nothing like it (nor do I go on this)
Popeye & Bluto's Bilge-Rat Barges® - WDW, Kali Rapids to the extreme + viewers with water cannons
Dudley Do-Right's Ripsaw Falls® - WDW, Splash Mountain X 3
Jurassic Park River Adventure® - Spash Mountain X 2 mixed with Dinosaur
Jurassic Park Discovery Center - WDW, Dinoland Boneyard
Pteranodon Flyers® - WDW has nothing like it
Dueling Dragons® - WDW, Closest would be RNR Coaster (DD is better & two tracks running simultaneously)
The Eighth Voyage of Sindbad® - WDW, Indiana Jones (but not...)
Poseidon's Fury® - WDW, Cant think of anything like it
The Cat In The Hat - WDW, Winnie the Pooh
The High in the Sky Seuss Trolley Train Ride - WDW, nothing like it
Caro-Seuss-el - WDW, cant think of the theme but a standard merry go round
Universal Studios
The Simpsons Ride - WDW, Nothing like it (anywhere), closest would be star tours on steroids with simpsons theme
Hollywood Rip Ride RockitSM - Not open yet so cant compare - OPENING 2009
Shrek 4-D - WDW, Muppets/A Bugs Life
Revenge of the MummySM - WDW, MT Everest
MEN IN BLACK Alien Attack - WDW, Buzz Light Year
Terminator 2®:3-D - WDW, cant think of anything like it
E.T. Adventure® - WDW, Peter Pan
Jimmy Neutron's Nicktoon Blast - WDW, Star tours in a theatre
JAWS® - WDW, nothing like it
DisasterSM - WDW, Backstage tour at DS (but much different)
TWISTER...Ride It Out® - WDW, nothing like it
Woody Woodpecker's Kidzone® - WDW, Toontown (+ water play area)
Express Lines
Disney Fast Pass - 1 ride per person every 2 hours
Universal Front of the Line Access - Most rides, all day when staying on-site or Most rides 1 time per day if purchased seperately when not on site.
Dining/Shopping/Clubs
Disneys Down Town Disney/West Side/PI (former) = City Walk (more food and clubs then shopping)