As a foodie and as one who enjoys ambience as an almost equal part of the meal, I love this topic!
I really like the atmosphere in a lot of the Epcot restaurants that have been mentioned (Le Cellier, San Angel, etc.), but a lot of them are VERY seat dependent and crowd dependent. Visits at these places are fantastic if they are not crowded and you get a good seat, but they can also be a lot less enjoyable if they are crowded or you end up in a bad seat.
Worst case scenario was being at a table for two at an extremely crowded Le Cellier. I didn’t mind the smaller table as it was just my wife and I, but our small table was sandwiched between two other tables on both sides of us. We were less than arm’s distance away from the other tables and all of the conversations could be heard by all of the parties (even a low level speaking). It totally negated the charming and romantic atmosphere.
We’ve also had the exact opposite experience at Le Cellier where on another visit the restaurant was quieter and less crowded and we were seated in a large corner booth, allowing for a much lovelier and intimate meal. It was a completely different (but wonderful) experience than the one mentioned above.
And I would say that most of the Epcot restaurants are hit-or-miss in this way as very few have much room between tables.
I don’t think Monsieur Paul was mentioned, and while the interior isn’t as “unique” in terms of special theming, it had a beautiful and elegant exterior that completely matched the upscale dining, and it’s one of the few places in Epcot that seems to have slightly more breathing room between tables. It doesn't seem to be all that popular of a restaurant, but a birthday meal at MP last year has easily been my favorite meal at WDW.
Space between tables is one of the reasons I tend to prefer the resort restaurants; tables are given much more generous space and some of the visual theming of the signature restaurants is quite nice. I’d definitely list Jiko, Sanaa and Flying Fish as some of my visual favorites, though I believe Flying Fish will be undergoing a reno early next year, but I don’t know to what extent.