>gen 1 introduces us to the world of Pokemon and how things are going to work in the franchise overall
>gen 2 just gives you more of the same
>gen 3 properly adds legendary pokemon into the story and ties them to the antagonist gangs, setting a tradition that would last many games
>gen 4 pretty much adds more of this
>gen 5 connects the player to the legendary pokemon and the gang in a more meaningful way other than being just a power tool
>gen 6 basically repeats older gens again, a step back
>gen 7 makes you befriend and protect the legendary in several parts of the story and redefines antagonist gangs and true villains
>gen 8 kinda goes several steps back again, except you focus on the third legendary first
>gen 9 sets up the legendary as your main partner, makes it part of your friend group and gives it a character arc to complete against the true villain
If you wanna experience the true progress of Pokémon's stories you gotta play the odd numbered generations, even numbered ones will only grant you a rehash of previous experiences. Prove me wrong.