I have been to Orlando several times in the past, so it won't be a brand-new experience. However, it's been 3 years since I was at Sea World and Universal and 9 years since Disney, so I know there will be some new things that I don't want to miss. Any tips on must-see or must-do experiences are welcome as well! There will be no young children; 4 adults and one 15 year old.
Now I would double check on a couple of dates due to them being moved around this year at WDW. Yeah, for some reason, WDW has moved some of their events around a bit.
EPCOT and DHS will be pretty crowded on the weekends. Why you ask? Its because of the Flower and Garden Show and Star Wars Weekends. Locals enjoy both very greatly for some reason! Both events are alot of fun, especially if you are a Star Wars fan.
Since you haven't been there in 9 years, make sure to set aside some time to go see Fantasmic which only plays on certain nights. The whole family will love that! As for the 15 year old, DHS and Animal Kingdom are the ones with the big thril rides (if they are into that!)
Also, I do not know if I didn't catch it, but are you staying at some resort while down there? You get perks at Disney and Universal!
The first was weather. It rained. A lot. Not talking a few showers or something, no, I am talking a purely absurd amount of rain. Not sure if that is normal that time of the year or not, but the amount of rain made it impossible at times to do anything (no amount of rain gear was appropriate for this amount of water.)
Second was the large amount of school field trips we saw. Which meant that the parks were sometimes crowded during the week with a bunch of unsupervised kids running around.
Overall, I liked the week (when it was not raining, it was quite awesome), but just keep in mind you might have some issues to deal with.
If you know its going to be a rainy day, I would suggest EPCOT since most everything is indoors
Anthony mentioned seeing Epcot if it rains. I disagree. Although Future World is a viable option, the World Showcase is best seen on a beautiful day. You'll appreciate the various ethnic drinks, too.
If you can afford it, I recommend staying within the resort you'll be visiting most. There are incredible perks to be had. Also, dine outside of the parks. Epcot, Disney's Hollywood Studios, and Islands of Adventure have pretty good dining options, but better restaurants with on-par prices can be found at the resort hotels and CityWalk/Downtown Disney, not to mention downtown Orlando.
I'm not sure how the crowds are in late May, but it's always a good idea to get to the parks early, preferably at or before opening time.
My #1 tip: you can't do everything. If you're hot, tired, cranky, bored, or any other variation of miserable, leave the park. Don't force yourself to see everything. I cannot express this enough. I enjoy getting to the parks at opening, leaving before 3, taking a nap at my resort, having a swim/shower, and drinking cocktails in the room (especially if you have a balcony) before returning to the park at night for fireworks, missed attractions, and/or a late dinner. The temperature is cooler, the crowds are thinner, and you'll feel refreshed and ready for more.