In a game that is played out to larger city sizes, coastal starts suffer from hammer starvation compared to inland starts. If you are going for a cultural victory, they also suck for finding places to plop great artists. There are other drawbacks already mentioned, such as their vulnerability (if that can be exploited - the AI isn't nearly as good as a player at that).
Regarding sea resources, yes, having many sea resources, taking god of the sea, and building the harbor and seaport and lighthouse... kind of makes up for it, but also represents a huge investment just to get to good. When getting a coastal start, I hope most of all for 0 (zero) sea resources. This translates into a high number of bonus resources (like stone or sheep) on the land tiles and a stronger early game.
Regarding sea resources, yes, having many sea resources, taking god of the sea, and building the harbor and seaport and lighthouse... kind of makes up for it, but also represents a huge investment just to get to good. When getting a coastal start, I hope most of all for 0 (zero) sea resources. This translates into a high number of bonus resources (like stone or sheep) on the land tiles and a stronger early game.