Castle Crashers is, well, a special case...
1. It was the second game created by the Behemoth. And a totally different one from their first! The company was just starting, it was a very small team, and they had ONE artist. ONE. Dan Paladin drew EVERYTHING, all right? BY HIMSELF.
2. It is the best rated game in the XBL Arcade! Four player coop, many characters, weapons, pets! A fun experience that is cheap, and family friendly. I've had many laughs with my friends, some who were shy of gaming and its complexity.
3. It's fun. So there are many guys with arrow magic? So what? So there are a couple pets that don't seem that useful. So what? There are enough options to please anyone.
The Behemoth team created a solid game. Not a perfect game, but certainly, one made with all the effort they could put into it, considering their limitations.
In the end, many things were cut, many ideas scrapped, many things simplified. It's not easy making a game, yet The Behemoth did it, and succeded.
Does the game have a lot of potential? Heck yeah! I bet six more months could have made it even better! Still, what we get is good enough.
If you still are not satisfied, wait for Battleblock Theater, or Alien Hominid. The gaming world is large.