I picked this up a few weeks ago for like $15. Might be a little more than that now.
Anyway, it's a pirate standalone using the MB engine. There are land battles and sea battles. Unfortunately it's still in alpha so some things aren't working. There's no taverns yet so you can't recruit heroes, buy books or sell slaves. I don't think you can upgrade troops yet or ask your prisoners to join you yet.
Anyway, it's a bit tough at first, like Warband but even harder since you can't get bonuses from heroes.
It's actually pretty hard to find any discussion on the game, since Carribean is an incredibly common google search term, so it's generally limited to the steam forums.
Anyone else playing this? I'll post some tips later on when I'm not writing from the shitter.