so with that info (mid-20s no kids) here is my take on your must sees (i'm sure i'm going to leave things out as i'm doing this off the top of my head):
MK must sees:
--Splash Mountain (my favorite ride in all WDW)
--Thunder Mountain (i hate thunder mountain, but you should try it, you might like it....i LOVE roller coasters, but thunder mountain is not the up and down kind, my personal preference)
--Space Mountain (basically a wild mouse in the dark)
--Mickey's Philharmagic (really beautiful 3D animation)
--Stitch's great escape (i think this will be open when you visit - this replaced alien encounter which was good, so maybe this will be good too)
--Pirates of the Caribean
--Haunted Mansion
--Enchanted Tiki Room (not just singing birds)
--Buzz lightyear (a cute shooting ride - you can miss it if you're short for time)
--Wishes - the fireworks display....a definite must see...
MGM (we like MGM much more than universal):
--Tower of Terror (my second favorite ride in all WDW - this one is spectacular....a MUST MUST MUST see)
--Rock and Roller Coaster - a great coaster....smoooooth
--Star Tours
--MuppetVision 4D (the preshow on the tvs is very funny...also, look around at what the boxes and stuff have written on them)
--indiana jones stunt show
--Catastrophe Canyon (not the right name but i can't remember the name....interesting and fun)
--Great movie Ride - kind of cheesy, but my 17 and 19 year old like it, so maybe you will too
--Little Mermaid (not just for kids -- the puppetry here is very impressive...i like this one a lot and i'm not a kid)
--Sounds Dangerous
--Fantasmic (the nighttime fireworks, but a whole lot more than that....)
Animal Kingdom must sees:
--Festival of the Lion King (must must see)
--Tarzan Rocks (also a good show, but if you can only see one, see festival of the lion king
--it's tough to be a bug
--Kilimanjaro safari
--Kali River Rapids
--Dinosaur (fun ride with a cute preshow)
--flights of wonder (very interesting live bird demonstration)
--there are two long animal trail walks that we love but i can't remember the names
Epcot must sees:
--Mission Space (if you have motion sickness, save this for last)
--Test Track
--Spaceship earth (only if there is NO line at all)
--Universe of Energy (ellen degenes is VERY funny)
--journey into the imagination
--Honey i shrunk the audience
--Norway (if there's no line)
--American Adventure (if you're the patriotic type - i am so i like this a lot)
--innoventions east and west (some interesting displays - the ultimate home theatre makes me drool every time....and the tour of the automated house does too)..
If you like waterparks you shouldn't miss Blizzard Beach (typhoon lagoon is also nice, but BB has the better slides/etc. -- typhoon has the best wave pool)
Islands of Adventure must sees:
--Spiderman (i hated this, but everyone else in the world loves it)
--Jurassic Park (i liked this - i love log flumes of any kind)
--dudley dooright (another fun log flume)
--Hulk Coaster - excellent coaster
--Dueling dragons (way overated - i thought this was terrible in comparison to the hanging coaster at cedar point)
--popeye and bluto's bilge barge or something like that...raft ride..you WILL get SOAKED...
--the jurassic park visitor center....a nice reproduction...
Universal Studios must sees:
--Shrek 2 (ok, but not as funny as muppetvision at MGM)....
--terminator 2 3D (everyone raves about this but i didn't like it at all)
--jaws (corny but we loved it...our boat driver must have been on uppers...he was excellent)
--earthquake
--revenge of the mummy (new....fun coaster type thing...)
--Men in Black (fun shooting game but i wish they'd take the spin out of it)
--Back to the future (people love this, but i didn't)
--gory make up show (that's not the name, but i can't remember it.....it's very funny)
Twister - (this was the worst thing i've ever seen....totally stupid , but i'm putting it in the list because everyone else i've ever talked to thinks it's great)....
i've only included the must sees....i'm sure i've left some out...
others i've left out on purpose...