I'll be rating all Pokémon that exist at the time of writing.
Things you need to know:
1. I haven't played the mainstream Pokémon games besides few times with PokeMMO, my only real experiences with the franchise are Pokémon go, Pixelmon mod in Minecraft, and however much of the series I saw as a kid..
2. My ratings are mostly based on design and other such details, I don't know, nor do I care about how good they are in games.
3. This is for fun, and though it will reflect my opinion regarding specific Pokémon, don't take it too seriously.
4. I used ready made tier list thingies, so the quality is what it is, and if I'm missing Pokémon, that's why,

I was originally going to rate each one with number and few words, but that project kinda just died, so I did this instead.

Gen 1

Gen 2

Gen 3

Gen 4

Gen 5

Gen 6

Gen 7

Gen 8