It's about as good an RPG as it is a TV show, or a way to spend hundreds of dollars on cards. If you drew a parallel between games and music, this would be the ridiculous bubblegum boy band that has no talent whatsoever and barfs out albums that essentially repeat the same song over and over - and still sell millions of copies.
I'm not entirely sure if this game was a cynical marketing ploy from the start or if it just turned out that way, but from my perspective pretty much every element of it was designed to shift units and sell plushies (and posters, T-shirts, cards, lunchboxes...). Aside from the fact that the only theme of the game is "Collect 'em ALL!" consider, for instance, the fact that two versions of this game were released; both exactly the same game with a few places where you meet different Pokemon in each version. (Of course, I must add that I could be wrong, and this was actually a move on Nintendo's part to give kids a sense of interdependence and community.) Of course, after this became an unprecedented success, Nintendo realized "Why make people buy TWO different collectible versions when we can make them buy SIX?"
We all know that games are made to make money. But some of them accomplish a few other things as well, and sometimes they accomplish them better than they do bringing in a profit. This game accomplishes nothing else. It doesn't even have all that much to offer in the actual "game" area - combat is hideously repetitive (reminiscent of Mystic Quest without Mystic Quest's limited appeal). The idea of catching and training monsters would seem very original if you forget that it was created to sell toys of the monsters. There is actually a large number of extra side-quests/odds and ends, but honestly - the only reason you'd do them is to desperately keep yourself from realizing how insipid the game actually is. And the plot is bad even as far the "little kid tries to hard to beat cool kid and win contest" genre goes.
Ah, Nintendo. They've made selling out into an art form.