I first saw this on Netflix, and there is a very different synopsis there than on here, but even taking that into account, it's not completely wrong. Also, people are being way harsher on it than it deserves.
I thought the story was great overall. Was a certain character's backstory introduced a bit late? Sure, but it didn't ruin anything. The romance was the best part and how Geo Ddong became a part of the crew. The second lead couple had a good story as well, though her personality wasn't as appealing. But he loved her, so what can I say? I love the actress though, since I also saw her in Business Proposal.
The music is also really good, though I am slightly biased since one of the OSTs is by Yesung "Drawn on the Heart." A really beautiful song that made me melt during the romantic scenes.
I don't know what else I can say, just that I'd be happy to watch it again, and think it deserves a better rating. Give it a try!