Gen 1 since it started it all, the rest felt pretty much a 'copy/paste' with new skins and updates.
So you're telling me you just don't like the core concept of a sequel then? Because, like, Pokemon is no more 'copy/paste' than your average game franchise. An entirely new world with new sprites and new animations, a new story with new music and usually a significant portion of new characters/pokemon, new gameplay features and side content. Etc. Etc. Etc. While yes, subsequent generations DO in fact reuse the pokemon and moves from prior generations, that's less 'copy paste' and more 'building on what is there'.
There's nothing out of the ordinary about the way Pokemon goes about its sequels. Same base gameplay with tweaks and a new world/assets/story. That's how most games do their sequels. Nobody's going around saying that Super Mario Bros 3 is just the first game with copy and paste gameplay, despite it basically being the same running and jumping, fighting goombas and koopas, shooting fire, going down pipes, etc.
Kinda shocked more people don't like Generation 5. First generation that basically started from scratch with a fresh, new 150 pokemon (Many of which ended up being among my all-time favourites), by far the best story, and the last generation of the 'old-school' style (As in it was still marginally hard to paly and beat before all the quality of life improvements that made the game a breeze). They dialled back the crazy number of legendaries from gen 4, the starters were better, etc. Basically, Generation V was the refinement of Gen 1 I had been waiting for and to this day it's not been topped.
My rankings go: 5 > 1> 8 > 3 > 6 > 4 > 2 > 7
I didn't hate any of them but 7 was the only one I didn't love. Removing gyms and replacing them with the island trials just wasn't doing it for me. I did love how they did regional variants there, though I think they started that in Gen 6.
My Console Library:
PS5, Switch, XSX
PS4, PS3, PS2, PS1, WiiU, Wii, GCN, N64 SNES, XBO, 360
3DS, DS, GBA, Vita, PSP, Android