Brunswick Country Club is FANTASTIC. The renovation work - with enhanced green sites and re-sized greens - has brought a lot of interest back to the old Ross design. And greatly enhanced drainage. Really good. Played it in January and look forward to playing it again.
I am ambivalent about Frederica. It's pretty, and the experience is very nice. Great residential community course, but not on par with Seaside and Ocean Forest, IMO.
I like Plantation a great deal, but Seaside just has all the visual and strategic thrills of the classic Sea Island. I'm not sure I agree that the worst hole at Seaside is better than the worst at Ocean Forest, and my knock on OF is that, while the natural setting is magnificent, the golf course is not really integrated into it that well. It simply unfolds beside it. Nitpicking, I know. The most prestigious round on the island, to be sure.
Retreat is a fun little course. Used to be called The Island Club and was originally laid out by Joe Lee - I played tons of high school tournaments and rounds there. Has benefited greatly from Love Golf Design.