Oh Gosh, I love Disney, but there is so much that I would change/get rid of/update if I were in charge.
First off in Magic Kingdom:
I would get rid of the following and replace them with other rides based on things such as Wreck It Ralph or Big Hero 6 or whatever else: Tiki Room, Swiss Family Treehouse, Country Bear Jamboree, Tom Sawyer Island, Frontierland Shootin' Arcade, and Stitch's Great Escape.
I would definitely update the Buzz Lightyear ride; the guns suck (especially in comparison to Woody's ride!)
I would also update Jungle Cruise. I think the animatronics there are the worst in all of Disney World.
I'm not a huge fan of the new carnival set-up in Magic Kingdom either, but maybe that's because it's mostly for meet-and-greets (and I can't stand hugging strangers in Mickey costumes)!
I would remake Hollywood Studios almost entirely. That being said, it's my second favorite park (after Epcot). I love it, but it needs some serious work. Thank goodness they're getting rid of the American Idol thing. I hope they put something awesome there. The toy story and muppets areas are my favorite in the park, and I think all of HS needs to be as exciting as those areas. As you get closer to the Backlot Tour, you REALLY start to feel as if you're walking into the backlot. (This is not a compliment!) I'm not a huge fan of the shows, but that's probably just my personality. Still, sitting in those huge arenas sweating my skin off and straining to hear whatever the tiny, little people on the stage are mumbling through a microphone is not fun. I think Toy Story fit so nicely in HS that I wouldn't mind seeing other PIXAR rides there, you know? If Disney won't put a decent Stitch, Wreck It Ralph, Incredibles, or Ratatouille ride/attraction in Magic Kingdom, why not put it in HS? My family and I talk all the time about how Hollywood Studios should be a mixture of Starwars, Pixar, and Marvel. (Ironman coaster, anyone?)
For Epcot, I just wish they would put something in all those unused pavilions. I also really hate the innovations centers; they'd be nice if there was actually anything to DO inside!! Other than that, Captain EO needs to go. Worst. Thing. Ever. And that's closely followed by the Lion King Circle of Life show or whatever that is. Terrible! (And while I'm at, I just want to say that I really wish they hadn't changed Test Track. I thought the whole test dummy idea was so cool. The Chevrolet blue is pretty and all, but it just feels like riding inside an advertisement. Lame.)
Finally, I don't have much to say about Animal Kingdom. I really dislike the entire park. Zoos aren't my thing, so I can't really have an opinion on a park that is, well, a zoo. All I know is that Avatarland sounds like a huge mistake and a terrible idea. The whole Avatar phase was over in a couple of months; when is the last time you heard anybody praising it? Bad call Disney.