>>53821832NTA but as a bort i think gens 4 and 5 are both the best executions of the modern and classic styles of pokemon.
gen 4 combines the day'night from gen 2 with gen 3's contests and new mechanics, with a slew of new evolutions giving much needed boosts to old pokemon and the physical/special split making more pokemon and moves viable. they bungle bases, but there wasn't much to do with them back in gen 3 anyway and the underground is cool. gen 4, or specifically platinum, is the best way to experience classic pokemon.
gen 5, similarly, is the best way to experience modern pokemon because it doesn't fuck everything up. the rivals have character (unlike gen 6), the interruptions aren't too overbearing (unlike gen 7) and and the story they tell is decent (unlike the ones that aren't gen 7) and the games are balanced so that infinite tms and smaller gym teams don't make the game a cakewalk (again, unlike gen 6). it was also the last time we had over 100 new pokemon, most of which have stellar designs.
tl;dr the thing gens 4 and 5 have in common is being good games