Heres my idea of 'Ahab'
You start in a tutorial with a ship and small crew learning mechanics:
Ship tactics; have your crew take different positions to do different things and respond to weather and environment.
Spearing; how to aim for whales/other prey, using harpoons with different abilities
Movement/Navigation, etc.
Selling/recruiting in towns.
After bagging 2 whales, you meet the great white whale, which destroys your ship and all your crew and leaves you maimed. You start back in town on a dinky ship with just enough to run it, and a new stat called Madness. Madness is a good/bad stat which as it goes up gives the captain more strength and allows the ship better survival in adverse conditions, but as it goes up the types of crew you can recruit changes and the events that happen run more to insanity itself.
You then scour the seas hunting and bagging whales and other sea creatures, slowly upgrading your ship again and recruiting. You eventually begin encountering mythical sea creatures and bagging them too, with new whale types appearing. Eventually new areas open up, which contain flying whales and ghost whales. You eventually plunge into hell itself where your ship must tread on lava (and any crew that fall in die, of course) hunting red lava whales and demon whales (and a host of other creatures). At the end, you confront the great white whale at the edge of creation, where an epic duel occurs (more epic if Ahab is completely mad by then and all his crew have abandoned him or died).
I think that would work.