I would buy Castle Crashers 2 instantly. I bought this game to play with my son and his cousins. After we finished it I tried to find another game like it we could move on to, but nothing matches up! Nobody has been able to create an equal or better game in this genre. To the extent that we ended up just replaying Castle Crashers 1 because it's still more fun than the other games in the same genre.
I also agree with the Angry Birds analogy, I have strongly considered buying merch from your store, but the shipping to Europe was a bit steep, otherwise, I would've bought the pluches already.
Another thing that would be analogous with Angry Birds is that I would already buy reskinned versions with different levels and story. E.g. a Star Wars version