@scribblemacher Having the running shoes is a pretty nice change from Gen 1, in which you had to wait for the bike to move faster. You also needed to use it from the Bag every time, there wasn't a shortcut button. I rearrange my inventory to put the bike or a rod at the top when I play Gen 1.
The biggest changes to Gen 1 Pokémon were introduced with Gen 2, which split the Special stat into Special Attack and Special Defense, and added Steel-type and Dark-type. Magnemite and Magneton were originally only Electric-type. They took less damage from special moves before the Special stat was split.
A bunch of Normal-type moves also had type changes. Bite, Gust, Karate Chop, and Sand-Attack became Dark-, Flying-, Fighting-, and Ground-type, respectively. Gen 1 also had moves which just didn't work how they were intended, like Focus Energy (and the item Dire Hit), even in Yellow.
Move lists are generally nicer in Fire Red and Leaf Green, such as Charmander potentially learning Metal Claw before Brock (although Geodude and Onix had such poor Special, you could get away with Ember). There were also bugs, like Eevee -> Flareon not learning Ember in Yellow.