I think one of the biggest reasons gen 1 & 2 are the best is their immersion, for example the learnsets, before gen 3's movebloat the pokemon actually had realistic movesets, for example in GSC your Heracross would use horn attack as its strongest move until its well trained and can use mega horn, in HGSS Heracross gets brick break at level 19. So Heracross, the "Single Horn Pokémon"'s strongest attack is a type of karate chop rather than a lunge with its great horn. It makes no sense. Completely immersion shattering and soulless. And this is just one example, pretty much all Pokemon suffer this fate in gen 3 onwards