Chadwick's is on the grounds of the South Seas Plantation Resort. It offers a different type of all-you-can eat buffet each night.
On the night we visited, the theme was seafood. Seafood usually doesn't lend itself well to a buffet--it suffers from sitting out for a long time, and tends to be overcooked. However, most of Chadwick's seafood was really good. The soup was a creamy lobster bisque. The cold seafood bar had several kinds of smoked fish, poached salmon, peel-and-eat shrimp, king crab legs, and excellent mussels and clams.
The hot food was predictably less than stellar, but not bad. There were deep-dried grouper and shrimp, oysters Rockfeller, and several fish preparations with different sauces. Although the fish tasted very fresh, it was overcooked and tough from sitting in a steam table for too long.
There was also a salad bar, which we didn't sample. We did try some desserts from the dessert bar, and wished we hadn't. Nothing was bad, but nothing was special, either. The key lime pie was too sweet and over-firm. The coconut cake didn't taste much like coconut and was a little dry. If I had it to do over again, I would have skipped dessert and gone back for more mussels.
Chadwick's wine list is not extensive, but quite reasonably priced (unlike many things on Captiva).
The atmosphere is casual. There is live (and loud) music in the bar on weekends. If you want to skip the band, make a reservation before 7:30. The band was just starting when we left at around 9.