You'll get lots of responses, so be prepared.
Here are our favorites over the years:
Skull Creek Boathouse
On many peoples' favorites list, this place doesn't take reservations but is still worth the effort. You can go early which sometimes helps. You can sit inside at the bar and get the same menu. Or you can go on a waitlist when you arrive and hope it's not a long wait. We've had good success with all three. Very good, fresh seafood, including one of the top low country boils around. NOTE: There is also Skull Creek Dockside which sits right next to Boathouse and, yes, owned by the same company. However, they are two different restaurants and menu approaches. Dockside is a bit more upscale and we didn't find the service or food to be as good as Boathouse. Some people like it better; we don't. Dockside sits in what used to be a Chart House restaurant; whereas, Boathouse has the ambiance of a local joint which we enjoy much more.
Fish Camp on Broad Creek
Excellent seafood, nice wine list, and sits near the water at a dock. Service has been excellent. You can sit inside but I recommend eating outside where there are plentiful fans during warmer weather.
Hudson's on the Dock
A bit of a caveat here. The first couple of times we went, it was very good and very fresh seafood. The last time it seemed to have lost a step; however, that could have just been an off night. I suspect you'll find a lot of people mentioning it as a favorite. It has the feel of a local joint with no real aesthetic to it, sort of a diner feel. But, the food has been excellent in the past, and the ambiance actually adds to the experience.
Scott's Fish Market
I mention this one primarily because it sits just over the small bridge right there at the resort, less than a five-minute walk. It's not great but it's solid, though it does have one of the better crab cakes I've ever had (have lived in Maryland and Alaska for the record). Very convenient.
Ela's Blue Water Grill
Another five minutes down the marina from Scott's, it's about the same quality, perhaps a little better, and they definitely have a better wine list. Haven't been there in a couple of years, but we enjoyed it when we went.
Social Bakery
Sits right beside Scott's, but it's a pasty shop. However, they do have quiche and other savory items. Very freshly made items, especially sweets, and while good, they're also pricey. Worth grabbing a dessert there after eating at Scott's or Ela's and taking it back to the room.
OMBRA Cucina
An upscale Italian restaurant about a mile down the main road, and it sits in a small (albeit tony) strip mall. It consistently wins BEST OF awards for the dining experience and the head chef/owner Michael. It's not a snooty place, just upscale casual. They have some great, authentic dishes and an exemplary wine list.
Finally, and this applies only if you have a 1BR or 2BR suite and feel like cooking. Get your own fresh seafood and cook it in your room. Barnacle Bill's is a very good place to buy off the boat seafood, and if that's not an option, the nearby Kroger and Whole Foods would have what you need.