But there wasn't really anything I had problems with in Generation 1. In fact, I loved that Mew glitch in Pokemon Yellow. How could you resist that cute Pokemon!
What did Generation 1 had that Generation 2-5 didn't have? Well there is that Charizard weakness to Ice types. This is a toughie. I would say the glitch to get those secret/very rare Pokemon of Mew and can't do it to Celebi/Jirachi/Deoxys/Manaphy-Arceus/Victini in the others. That's about all I can actually remember :/