Tough one. Pretty broad question. But I'll give it a try.
First, the shows: IOA: The castle light show is not to be missed. It is short, but awesome. If you like super heroes, it is pretty cool to be down near the Spiderman ride when the villains are out. Green Goblin and Doctor Doom are great, then the superheroes show up on quad cycles. For the long time Disney parks fans, it is similar to the old Power Ranger meet and greet at Hollywood Studios.
USO: Must do: The Hollywood Horror Make-Up Show & The Blues Brother. Both are a lot of fun, especially if you are an older Gen X'er. The Cinematic Celebration is good. I wouldn't consider it a must do, but it is pretty impressive. Animal Actors on Location is also pretty good as well, but not must do unless you are a total animal over.
Rides: IOA: Spiderman and Forbidden Journey are the two must do's, but I haven't had the pleasure of going on Hagrid's yet (2 weeks from today will be my first ride hopefully). Kong and Hulk are also good. And I actually love the Dr Seuss High in the Sky trolley. The water rides are fantastic as well, especially Dudley Do Right which is the fastest log flume ride I've ever been on. But you get soaked to the bone. As wet as jumping into a swimming pool totally clothed. I'd suggest making a plan to do that wearing swimies and dry fit shirts then heading back to your hotel to change clothes. The Hulk is also great, especially at night.
USO: The Simpsons and Men in Black are my two favorites here. I can ride those over and over again (and will on at least one of my park days coming up). After than, Gringotts is must do because it is a spectacle. The ride itself isn't anything special though. But the presentation is awesome. Then The Mummy, which is a lot of fun and pretty exciting, but not too crazy. Rip Ride Rocket is a lot of fun as well because you get to pick the song you listen to during your ride ("Sabotage" by the Beastie Boys is the best), but the seats are pretty tight and uncomfortable for larger folks (I'm 6'3" 245 lbs and barely fit).
Food: US is not as good as Disney when it comes to dining options. Most of the really good stuff is at the City Walk. But the Harry Potter restaurants are both great and offer some high quality meals. We get the feast that we share. IOA has Mythos (sit down) and Thunder Falls Terrace (chicken and ribs - with a great view of everyone splashing down on the final Jurassic Park drop). The rest of the places are average theme park cuisine. USO has Krusty Burger and the Taco truck along with Lard Lad Donuts. After that, nothing excites me much there. The Citywalk has some really good spots though. Almost every place is good. Red Oven in the BEST pizza on property and a fantastic place to people watch after the parks close. Antojitos is standard Mexican, but good and reasonably priced (and filling with the free chips and salsa). And Pat O'Briens is great if you like dueling pianos. The food is ok too, but nothing special.
Hope this helps. My world of advice is try to do as much as possible because what I like isn't neccessarily what you would like.
