What they have done with Seaside at Sea Island is really remarkable, IMO. I played it in January and loved it. Intriguing options, visually stunning, a man-made tribute to the local environment. I much prefer it over Ocean Forest. I have not seen the re-work at Brunswick CC, but the bones of a great course have always been there.
After the high-falutin' round at Seaside, my companions and I ventured over to Jekyll and Grand Dunes. Talk about bones of a great course! It is unfortunate the the full links has been lost, but Grand Dunes is a must-see, if only for the great Mae West par-5 fifth(?). The pitch shot sixth and the dunesy second and third are also great holes. As much as we enjoyed Seaside, our conversations on the rest of the trip centered around that little Travis/Ross niner. Not to mention the fun of having played Georgia's most and least expensive courses in the same day!
Oleander and Pine Lakes are fine courses, among the best values in America. As for Savannah, the historic Savannah Golf Club has suffered from uninformed architectural changes over the years, but where else will you find Civil War-era earthworks deployed as features (as on the 9th hole at SGC)?
I haven't yet seen Sanctuary Cove, but I am a fan of Osprey Cove in Saint Marys.
Finally, if you want to see a true hidden gem, make the 1-hour trip from the coast to Waycross, Georgia and play Joe Lee's little-known Okefenokee GC. I am biased, having spent much of my youth there, but it is wonderful golf course routed over scrubby sand hills on the banks of the Satilla River. Really, really good.