Well, Fresh *used to be* a must-eat on every trip - my favorite restaurant in all of WDW. Usually lunch, but once we had the Sunday brunch buffet. (Wow, we weren't expecting that one - didn't realize Sundays were different - and more expensive.)
Why "used-to-be"? Well, it was a Mediterranean-themed buffet. Anything but the run-of-the-mill choices, the food was really good, and it was marvelous to sample a little bit of all the offerings.
Unfortunately, it's no longer a buffet - the food is still very good, but it's no longer possible to sample a little bit of everything. It was just too frustrating to pick one dish to the exclusion of everything else.
The atmosphere is "pleasant" with a nice view of the cove. I wouldn't call it "themed" at all.
Also, lunch is now only served "seasonally". I'm not sure what that means, but it was never very crowded when I would eat there, which was always during the low seasons. And I'm not sure that it has ever been open regularly for dinner - perhaps it's used for private group dinners, since S/D does a large convention business.
In short - you'll get good food there, but it's not the gem that it used to be.