In its current form, the game has Creative mode, where you play around with the tools to create your different vessels, Battle Seas where you get to take on ever increasingly more powerful NPC vessels, Versus mode where you can battle your own creations or those in the Steam Workshop and finally events that allow the Devs to pit players against special challenges.
There is another mode in the works, the one I’m most interested in, Voyage Mode, which potential will be more of an adventure style mode. This should also introduce sea monsters and the titular Last Leviathan.
Still in Early Access, The Last Leviathan has a way to go but even with what you can do now, it’s well worth £6.99 on Steam . Here’s the Official Trailer.