I've always liked Pokemon. Red version was my very first game. I liked the concept of monsters, both cute and ferocious, duking it out in friendly competition at first, but what REALLY been drawing me toward the series as of late are how deep the game mechanics are, and how creative you can actually be with your teams. I mean, it's alright to take down the Elite Four with only your level 100 Mewtwo, but it gets boring after a while. Seeing your First-Generation-Only team's double battle strategy where your Raichu uses Fake Out and your Technician Persian wipes out the helpless, flinching opponent afterward with Assurance play out perfectly is totally satifying.
I guess, for me, Pokemon was a game that I enjoyed as a kid for the mindless entertainment, but I enjoy it now for the amount of strategy, thinking and preparation involved, which makes the win ever so sweeter.