My list:

• Fun new trick mechanics
• New characters, with a ton of cameos from old characters
• New Story with the same craziness of the old one. Mind blowing twists left and right throughout it.

I had mentioned the following in this thread:

"If they were to make a sequel, perhaps they would just do it Phoenix Wright style and have it revolve around the same main character but with a very different overarching plot. Sissel's immortal and he has the asteroid still lodged in the shell that is the cat so other people who would die around that shell could also gain ghost powers."

This could be the way that new "trick" mechanics are implemented as you take control of other characters.

The Adventures of Missile