Going from my own personal experience, it depends on when you have dinner there.
My first time eating there, we went around 8pm I think, and it was mobbed, found it difficult to get a seat (its a cantina, so you don't get shown to a table), and the food was lukewarm (although there are microwaves dotted around the restaurant so you could heat your food up I suppose). I wasn't impressed.
Second time though, we went before the parks closed (I think it was around 6.45pm), and it was great - hot food, lots of choice, and plenty of tables free.
Both times we were there, we saw Goofy and Pluto in the restaurant too .