Not bad.Indeed the jump doesn't feel nice, the NES controller was 4 way, so it was not possible to keep up and go right and left, that's why most Mario-like games mapped the jump on A, only games like Castlevania use A and B for attacks and has the jump on UP and it's go straight up.
Edit: it was possible to press UP and RIGHT, it was just uncomfortable and not considered by most games (but Gradius was 8 way).