Underrated: Tokyo Dining in Epcot. I eat here nearly every time I'm at WDW and have never had a bad meal. The service is always great, the food is good, and even when it's full, it's never too loud for me to carry on a normal conversation with others at my table. That last point is a big deal for me...I want to be able to talk without yelling to be heard. It's relatively easy to get an ADR here and I've also had pretty good luck walking up without a reservation and being seated quickly.
Overrated: Via Napoli in Epcot. I was so excited to try this last time we were at WDW because of the rave reviews I'd read and heard from others. The first thing I noticed was how loud it was in there. We were a foursome seated at a table in the little side section, and I could barely hear the people sitting across the table from me, let alone the poor waitress, who was so soft-spoken, I had to ask her to repeat everything at least twice. As for food/drink, the bellini was good, but the pizza was so-so at best. Some parts of the crust were burned to the point that it was inedible, and the toppings slid off every time I tried to pick a piece up. I ate the pizza (minus the burned parts of the crust) because I was starving, but I left the restaurant pretty disappointed and wondering what the fuss was about.