I like Pokemon because it's childish, but at the same time strangely complex, as noted by the person a few posts above me. I first got into it when I was about 4, because it was the "cool" thing back then. I loved the anime until around age 9, when I started to hate Pokemon, thinking that the idea was "stupid". But then around age 11 I got back into it, playing the video games discreetly to avoid being pigeonholed at school as "that one nerdy kid". I just finshed my freshman year of high school a couple days ago. Surprisingly, a lot of people at my school play Pokemon. I also enjoy it because it's fairly easy to make the franchise into your own world. Finally, trading and battling provides endless fun. There's always a trainer looking to battle.
I'll conclude with this: Pokemon is merely an interest for me. I don't spend hours upon hours of playting it, I play it whenever I get bored or have free time. Deep down, I'm a sports and music lover.