Rouge is a perfectly usable character. Her sprites are pretty good, though shading/edges could maybe use a touch-up.
Her moveset is, well it's Knuckles moveset with some extra features. It's not my preference but it is close to how she plays in some games so I can't really complain.
She's got a lot of potential but as is I don't think she really adds much unless you were particularly interested in this moveset for her for a story line map pack or something similair.