Like any service industry, it is all about the management. If I encountered a bad server and the manager did nothing about it, I'd never return. Same with the food, etc....
the times I have NEVER returned to a place were always based on poor management. A bad server could just be inexperienced or having a bad night, bad food (unless it is food poisioning) can just be an off night in a kitchen or not to my liking...but if the atmosphere is bad and the management is bad, I'd never return, or if the place was just a rip-off for the money.
Places I'd never return at WDW:
Pizza Planet...dirty, poorly run, horrible food, waste of CS credit
Cosmic Rays..too loud, poorly run, horrible food
Chef Mickeys..too loud, poorly run, dirty buffet, over-booked
See...it all, to me, has to do with how the place is run. Being busy has nothing to do with it, that is not an excuse. There are places here in Chicago that are ALWAYS BUSY like Portillo's (a hot dog/burger/ribs regional joint) and I have never, ever had a bad experience there at any location I went to...but WDW places seem to fair poorly when they are busy and that is just bad management.