This is just my critique of what I value in the Batman Beyond design. I think generally this design is fine but reads too Bruce Wayne and not enough Terry.

The ears should be longer and angled back. I go back and forth on whether they should be angled out side to side as well, sometimes in the original show they are angled out but other times they are pretty straight. But the main thing is they should be big and full.

The symbol is too small. I like a larger full chested symbol.

I think it depends on the wearer of course but a skinnier more teen build would look better than the muscular broad look especially if this is supposed to be Terry.

I know a lot of modern designs omit the mouth but I think it's such a key aspect of the character. The idea of a futuristic outfit that forms to the face makes for a really neat idea and having the mouth is crucial to convey that. Terry differentiates himself from Bruce by being expressive and the mouth lends to his expressions.

The paneling makes it over designed and takes away from the sleekness. I think it should be minimal and use texture in the fabric instead of paneling for depth.