Contrary to what most fans say, I don't consider Black a great classic and RX a travesty. In fact I think the two shows complement each other: RX is strong where Black is weak (building up the plot and the tension over the episodes until the climax), and Black succeeds where RX is lacking (having a more intense, personal story). Black is a fancy car that keeps stalling whenever it gets running, things begin to happen plotwise only to languish as the show wastes time with filler. Even Nobuhiko is never really defined as a character: in one episode Kotaro remarks casually that he is very bright, which means he will be also as Shadow Moon. This happens very late in the show. On the other hand, RX has a weak start (and a mediocre sendoff for Shadow Moon), but starting with the Roborider-Biorider arc the pace begins to pick up slowly but surely. I also liked the idea of Kotaro building a "Bat Family" of sorts (with Reiko, Joe, Shigeru and Kyoko), even though it wasn't developed all that well. I consider Kotaro the Stephan Zweig of the Rider series (for anyone who has read his "The World of Yesterday", with Black being his WW1 and RX his WW2.)
You can argue that RX should've been its own show, but as it was it's decent. It's not the disaster fans make it out to be, and Black is not the perfect epic they pretend it is either. Watch Black and RX together, and have some fun.