Demo One gives a wrong impression of the game, since it is an exclusive level (not present in the final game). But the final game was more about the mazes and the light puzzles than the shooting itself.
If you like the shooting part, then Pirate Hell is probably the closest thing i've played so far.
If you like something exactly like Overboard ... i havent seen any. Except Overboard! of course, there was a PC port back in the day and its perfectly playable nowdays. You can even run it at high resolution and 60FPS (not recommended in some levels, since framerate is tied to a bunch of things).
BTW: There was going to be an Overboard! remake for Project Spark.