I've always been a really big fan of RPGs (dating back to The Elder Scrolls: Arena, The first few Final Fantasies, Breath of Fire, The Legend of Zelda, Secrets of Mana, ect) so it was a natural fit. Not only is it a really fun and addictive RPG, but it is very custom; by that I mean, you have 649 pokemon from which to make a party of six and, for each of those six, you choose four moves out of their entire movepool for their moveset. It can be played in so many ways. That really appeals to me. Factor in the fact that I was 9-10 years old when Pokemon came out here in The States, and you have someone who is tailor-made for Pokemon. I still play because not only do I still love RPGs, but I will always find a pokemon in the new gens that I like. I also like how they continually upgrade the series. It really makes me wonder how they are going to "up the ante" in the sixth generation.
Plus, it is a good break from all the survival horrors...