Whenever you travel through a cave, you hear that TERRIBLE sound of yet another bloody Zubat/Geodude.
Whenever you surf through the ocean, you hear that EVEN WORSE sound of yet another bloody Tentacool.
Breeding.
Type inbalance availability (Seriously, Rapidash or Infernape for Fire, and Wiscash, Gastrodon AND Quagsire for WATER/GROUND?)
All HM's except Surf and Waterfall being junk in battle.
Too high of a luck factor in the Battle Tower (Hi there Quick Claw Guillotine Crawdaunt, DIE IN A FIRE)
Some evolution methods
Bidoof
Yeah, I don't think too highly of the DS games.