I find your question tough considering Pokemon is diversified through different forms of media. To start; the video games give you a world to explore as well as catch creatures. You get to watch them grow, learn new moves, evolve, etc. through battling other Pokemon by way of wild, trainers or gym leaders.
Personally, fell into Pokemon through my brother and quite basically everyone else introducing me to it. I myself, being born in 90 got to witness the mass explosion of Pokemon on the scene. Pokemon incorporated various monsters from cute, strange to cool. So you could say, to everyone there were favorites, ones you wanted to own in-game, draw them and maybe even write a fan fiction incorporating them.
It was a glorious time and that time is slowly approaching again with Pokemon X & Y hitting shelves sometime in October. These are just my thoughts/opinions, but I wouldn't be surprised if more individuals rejoin or start Pokemon simply because of Pokemon X & Y. It has caught my attention to an excessive level, with every new Pokemon being revealed even more anticipation builds along with knowing about a new type, fairy.
I could keep going to discuss between TCG, fan fiction, etc. and make this longer, try to hit every topic within Pokemon, but my time has come to end this long post. For reading, thank you.