With WDW, I don't feel like I have many must-do's. We have a number of tend-to-do places.
Probably my #1 and #2 are the Yak and Yeti places. The TS is one of few places with good veggies at WDW. The QS fried rice is a favorite. It isn't as good as it once was, but it is something we tend to get.
Docking Bay used to be pretty good, but that too has gone downhill.
The best foods at Epcot, IMO, are the festival foods. The best of them is usually the Art festival, but that also was a step down last year. I'm hoping next year will be better, but I'm not holding my breath. Japan's booths often have something great. For more year-round options, I would tend to say Japan's options are good.
DS- I also like Blaze. Not a must-do, but good quality and decent pricing. For DS TS, I tend to visit is Cityworks. I wouldn't say it is super, just that it isn't expensive. If you join Bottleworks, you get coupons.
Oh, if you plan to visit Yak and Yeti, Landry's group offers a membership. It includes all Landry's: Rainforest, Bubba Gump, Joe's crab Shack, Mortons, Saltgrass, T-Rex, and more. There is a fee to join, so it only pays off if you will go multiple times, but for repeat visitors it is worthwhile.
I wouldn't call it good, but in MK Pecos Bill is one of the least bad options.
At the hotels, Topolino's Terrace is worth a dinner visit for the view at dusk/fireworks.
Though you said WDW, Thunder Falls Terrace is a must do (but soon to be changed from QS to TS). Confisco Grill has recently been great. Cowfish at Citywalk. Stella Nova's QS, esp breakfast. Offsite Pho 16 Express has excellent pho soup. Okayama was very good, reasonably priced classic sushi. I also like QS Lime in Flamingo Crossings. (not exceptional, but charming)