If you're looking for mainly atmosphere, I have a few suggestions...
1) Cosmic Ray's, when you sit near Sonny Eclipse... without Sonny it would just be cafeteria-ish... but with Sonny, you've got dinner and a show! There's also some really good food options for the value on the
DDP, especially for the adults - like chicken and ribs dinners.
2) Pinnochio Village Haus, sitting by the windows that overlook It's A Small World... you can wave to the people on the boats.
3) Casey's, where you can sit in "bleachers" and watch the giant TV, or eat outside with the piano guy.
4) Pizzafari, which has elaborately decorated themed rooms - check 'em all out.
5) Flame Tree BBQ, which has seating areas spread over a wide area on different levels - all outside, but some under small shelters (so it's not crowded and remains relatively quiet), and some near water... the ducks and other birds may be near, so it's great for animal lovers (but don't feed them or let them get too close to your food). Plus, they've got ribs - I love ribs!
I never really thought that much about the atmosphere at CS restaurants before... your question was one I enjoyed pondering. I'm sure some other people may have some other suggestions, and I'd be curious to find out what they are...