I hated Diamond and Pearl. The Pokemon were super lame minus 20 or so, and it was too easy. I beat the game with absolutely no grinding and I think I only used like 4 pokemon throughout the entire game, just because I didn't like the rest.
I beat the whole thing with just Empoleon, Luxray, Staraptor, and Lucario.
Less Pokémon -> more EXP for the ones you're using -> higher levels -> game becomes easier.
I beat Emerald once with nothing but a Sceptile and a Linoone; they were LV 60+ by the time I faced the E4, and I didn't grind.
"If you want to know what a man's like, take a good look at how he treats his inferiors, not his equals." -Sirius Black
While I haven't played B/W yet, D/P/P was by far the most forgetful for me, and I'm still trying to play the stupid game. I really can't remember pretty much anything about the game, as I've spent months on and off trying to finish it. I remember more from the one time I got through Sapphire when I played that 8 years ago, than I do from Pearl when I tried it 3 years ago and Platinum that I'm still trying to play now.. I don't play competitively, so "balance" doesn't mean much to me at all. Hardly any of the Pokemon available suit my cup of tea - Using mainly a Nidoking, Luxray, and a Arcanine a friend gifted me. Defog makes Flash seem like a good idea (it wasn't). But mostly, it bores the crap out of me.
Even though DPPT refined the mechanics heavily, it had a really depressing atmosphere (not intentionally by the designers) in that it felt like Pokemon was getting really stale, at least for me. Again, that's not to say it didn't have a lot of gems, but it didn't feel the same to me as gen 1-3 did (in that I was always excited and looking forward to playing more, here it felt like a chore sometimes), and eventually the gen 5 games.
Everything in life is a battle. Even peace itself is a battle to maintain it.