Original:
Pretty difficult as a solo player, but just difficult enough. The controls took some getting used to, but once I did, they felt great to play with.
Edit:
So I finally got a friend to play this with me, and it was a blast. Again, the controls took some time, but eventually we got used to them. It was very fun bickering with my friend, who would get to steer the ship and try to take the wheel from each other, only to then crash into something and have to repair the boat.
The enemies look great; however, I have noticed that the one-eyes scorpion things were not that dangerous. On the other hand, I feel like the tentacles might attack a bit too fast after they first spawn. Even when my friend and I were both on the cannons and prepared to shoot, it still hit the ship. This would feel very bad, as it punished even good gameplay.
For the rest, the actual movement felt great, and the environment looked beautiful. There is this weird loop in the bottom right of the level where there is a wall that needs 6 chests, but you don't actually need to open it. Some chests were also very difficult to differentiate from the environment.
The combat itself felt great; the boss was easy at first, but quickly got harder as more bullets spawned.
All in all, I think this game is a fun party game that has a lot of potential. With more levels and maybe new mechanics, this could be a really fun play-through game with a small group of friends.