I've only eaten inside at FFB twice. Had the Krusty Burger, but had them hold the liquid cheese. It was a good burger, better than what I'm accustomed to at theme parks. Very messy, even without the cheese. The fries are fast food curly fries. No more, no less.
I preferred the Chicken-and-Waffle Sandwich, which comes with some kind of maple syrup-mayo mix. Sounds awful, but was actually a great dipping sauce for the tater tots.
I liked both sandwiches, but probably would get the Waffle sandwich again. I know these are the two items that get mentioned the most, so I'd also be curious what other dishes people have tried.