Mythos' menu has become rather bland. Even still, i go there for the aesthetics of the building itself; the food is almost an accessory. I do miss some of the old dishes, but even still going to IOA without going to Mythos would feel wrong.
Food wise, my favorite restaurant in both USF parks is Finnegan's. The looks are nothing special, typical Bennigan's visuals, but any park restaurant that serves corned beef and cabbage as well as bread with apple butter is a great place to go.
That being said, my absolute favorite park restaurant is probably the Liberty Tree Tavern in the Magic Kingdom. You get to gorge yourself on a huge spread of Thanksgiving style food, while surrounded by characters. It's not cheap, but for all the food you get, especially within the confines of a theme park, the price isn't too bad.
My top two snacks are also at Disney parks: Pineapple Floats in MK, and chocolate covered frozen bananas in all the other WDW parks (unfortunately MK doesn't have them).
