The characters themselves are alright, I think, aside from being somewhat repetitive (Many characters, like Dad, Karkat, and Kanaya, have to run in close to their opponent to deal damage as fast as they can with a close-range attack. Characters like Roxy and Jade with bigger attacks and a more unique playstyle/use feel more fleshed-out as characters as a result.) I might be wrong about some of that, though, and that's the thing: I mainly found them lacking simply because I didn't fully know how to use them or what they did. I really liked playing as Roxy, but I couldn't consistently use her perfectlygenericobject-punch attack and ended up having to just run in and mash A and B. The biggest thing you can do to help your game, in my opinion, is add some explanation of how different characters work- what their moves are, how to use them (are directional inputs involved?), and maybe a general playstyle.
I totally approve of making Jade a really good character- the movement stuff she can do is some of the most fun I've had with a game like this!