Well, if you're referring to the anime, it's the worst representation of the Pokemon series. Even Satoshi Taijiri himself said so. The games are still going pretty strong with the introduction of Diamond and Pearl. Diamond and Pearl attracted a lot of new Pokemon fans. Most people look down at Pokemon because they haven't seen what Pokemon really is; they're judging upon the worst representation of the series (the anime). And automatically they won't give Pokemon a chance. It has grown to be more childish, but look at the games. The games are still going strong with complex values and hidden features. Sure the cute, furry creatures and the big, cartoony monsters detract from Pokemon's maturity level, but once you actually get familiar with some of the better aspects of Pokemon, it's actually pretty sweet.
Pokemon is now more popular than it had ever been after the release of Diamond and Pearl, and many suspect that Platinum is even going to go further and break DP's sales record. It's growing fast.