>>13159315adding on to that
Gen I: Started the franchise, No linearity after arriving to Lavender which is a GOOD thing
Gen II: Got to visit another region albeit an empty one (as a kid is was awesome as fuck though), added evolutions for some old pokemon, and the first battle tower.
Gen III: Added secret bases and contests both really fun side things, added the first battle frontier, two pseudo-legendaries not just one
Gen IV: Overall best music of the entire franchise, introduced GTS, Pokemon follow you, underground was fun as fuck, best champion ever and the first female champion
Gen V: Shook things up a bit with the plasma story line, lots of new Pokemon and even though there's a lot of quantity there's a lot of quality, PWT was much MUCH better than the battle subgay, the music rivals Gen IV for best music of the franchise.