The problem with Pokemon is Nintendo's Modus Operandi: Find something that works, remake it until it dies, Then cast Animate Dead on it and use it as a zombie.
Mario
Zelda
Metroid
CastleVania
Pokemon
It's all the same. All these games should have been dead a long time ago: name anything that's improved on Mario other than the graphics. It's still the same game I played on my game boy.
And Pokemon has joined the lot. I loved Red, Blue, and (to a lesser extent) Yellow (RBY). Gold, Silver, and Crystal (GSC) were pretty cool, but the whole "Chase down Raikou, Entai, and Suisune" was annoying as anything. But they were still pretty cool.
But while I played Ruby, Sapphire, Emerald (RE), and later FireRed and LeafGreen (FL), by that time it had gotten ridiculous, and without any innovative content.
RBY introduced something that I hadn't seen before in a RPG: a team that you can switch around freely for the best effect, and that had a core mechanic, rather than story, to explain how your team grew.
GSC introduced more of that: Berries and other holdable items, specialized PokeBalls, baby Pokemon, a day and week cycle, and (IIRC), Pokemon powers, and Dark Pokemon (The best thing, IMO), and in crystal, the Battle Tower. The extra 100 Pokemon weren't all that bad: especially given that they needed to with 2 new types.
But RSE was downhill. Team Rocket disappeared, all of a sudden, you couldn't get all the Pokemon with just a Game Boy (you needed Colosseum, and several other games requiring a non-portable game), and the world as we knew it disappeared. Oh, and the Day/night cycle is gone, you have to plant berries, there's more berries that you can hope to keep track of, all for a (Mostly) useless side quest. And what do we get in return: another 135 pokemon, and the ability to fight 2 on 2. Wow. There weren't even any really cool pokemon in the new set: I can name a few (The Weather-effected one, Shedinja, and maybe a few more)
And as such, I refuse to buy a DS just to play Diamond and Pearl. Maybe is someone can get me an emulator for PC, I might play, but I'm not even sure I'll do it then. Too much has been lost, and it's lost the sense of innovation that brought be to it in the first place.
And it's not just the video games. The CCG died when they started making new cards that were way better than the old ones: the original Haunter had 2 attacks, one that put the opponent to sleep and did 0 damage, and another that did 50 damage if they were asleep; a newer one is just the same except it's attacks to 20 and 60 damage (instead of 0 and 50). Other cards run in the same vein.
And honestly? I would go back in a minute if someone could demonstrate that Pokemon was doing something innovative and new, rather than beating the zombie horse again. But somehow, I doubt it.
Edit: I forgot. My favorite:
Houndour/Houndoom. Something about killing a RBY Alakazam lvl 100 with a lvl 5 Pokemon endeared me to this Fire/Dark dog. And gave me another reason to hate RSE: you couldn't get it.