I really wish Castle Crashers had more levels. So many possible designs and opportunities to make the story longer that just slipped through the fingers of Behemoth.

Like my idea in the pictures. They literally showed a Kraken in the background of the boat level, why not have a 2nd level where you have waves of the fish people jumping out of the water to attack the boat, and after a few waves the Kraken appears and you have to attack it's tentacles that are ripping the ship apart, and you have to jump over sweeping tentacle attacks that sweep the deck of the ship. This boss fight could just be a timer where you just have to survive for say 1 Minute 30 seconds on Normal and 3 Minutes on Insane. And the "Health Bar" is the boat itself and you just have to make it till the end of the timer to win and make it to shore of the desert.

Other missed opportunity levels would be having a Dark Castle level after the cemetary/swamp levels before going up the mountain to the ice levels. Definitely could have had the Skeleton minions as enemies and the peasants could have helped you storm the castle where the Necromancer Boss could have been placed at the top of the Castle.

Or an Ice level where there is a snow version of the Troll mother Boss from the forest but the minions are snow trolls with ice abilities

All kinds of other possibilities aswell

I finished the game with my Wife and we just felt kinda underwhelmed by the fact we crushed the entire story in about 3 and a half hours.

I understand that Insane is much more difficult but still.