I enjoy stream lined heroes, simple enough costumes, and mature, engaging, character driven plots.
Kamen Rider Black kicked *ASS* in those regards.
Kamen Rider Black RX, I will say, is NOT a bad show....but its no where near as good as Black and really, REALLY doesn't gel with me for being a sequal.
I don't like RX purely because it is a sequal. Now if it was in an alternate universe, I'd be quicker to accept it. Or hell, if it was an entirely new Rider series, even better.
But it just doesn't WORK as a sequal for Black.