Our family had dinner at CoCo's while we were vacationing on Tybee during July, 2013. All four of us enjoyed our meals. Everything was fine, but we can't say it was the best seafood we've ever had. We tried the crab cake dinner (my personal favorite), combo dinner with fried shrimp and scallops, grilled shrimp, and mojo mahi. Service was excellent - very pleasant and our food arrived fairly quickly.
The place is comfortable/casual, but showing a little wear and tear. All in all, a good, casual place to enjoy a good meal. If you're going to be on Tybee for at least several days, you should give CoCo's a try, along with the other higher rated restaurants on the island.