I think anything gen 4 and after looks terrible.

Greninja looks terrible? Decidueye? Xerneas? Pyroar? Tyrantrum? Aegislash? Trevenant? Aurorus? Vivillon? Zoroark? Luxray? Primarina? Mimikyu? Electivire? Leafeon? Gallade? Torterra? Infernape? Lucario? Lycanroc? Vikavolt? Passimian? Krookodile? Bisharp? Golurk? Braviary? Volcarona? Mudsdale?

Yeah, sure, every single Pokémon from number 387 to number 807 looks terrible.

It was simplistic design, sure enough, but at least everything was easily identifiable in terms of what's what. When one looks at the pokemon from the newer generations, if you haven't played them, you'd have no idea what falls into what type with most of them. Especially since practically everything falls into multiple categories now.

The old design philosophy was smart, even if it was quite basic.

You say that you're being objective because you're not affected by the nostalgia of gen 1 players.... but really you're just being affected by your own nostalgia of the gens you grew up on.

Look, as an objective opinion, gen 1 was really conservative with their designs. They used iconic animals and insects and just made them into poke. As someone who played gen 1 at launch, what I noticed specifically was that as the gens continued, it seemed like there was less focus on making a clever name and clever design, and more of a focus on "cool". I think, for those of us who grew up on gen 1, since we are older, we've also kind of grown out of the "cool" phase. Additionally, newer pokemon have this kind of human quality and facial expressions that most of us didn't really like from the gen 1 types that did. Nobody liked mr mime or jynx...the popular ones just kinda looked like animals.

I'd say if you really want to understand the difference between the gens, just look at what seems to make gen 1 look more like actual animals or things, and what makes later gens seem more like cartoon characters. Later gens just kind of feel like they have "accessories" or "flair", yaknow like they thought they were too bland or something. They just feel kind of overdone.

gen 1 feels chill.
later gens (3 and up) feel extra.'

EDIT: Just as something I noted right now, I think the thing about gen 1 was that it introduced this kind of world where common animals could be something more. It kind of gave real life this kind of magical undertone, like hey that mouse might be a rattata. Like, we were living in a world where maybe we were overlooking the common things we see every day. As the gens progressed I feel like pokemon became less about fantasy undertone. I feel like that's kind of a reason why pokemon go was so popular with gen 1 gamers, because it reintroduced that magic. The feel is just not the same in later pokemon generations.

What is breeding? There was so no such thing in Gen 1.

I personally like the simplicity of the Gen 1 designs, "there is beauty in simplicity". Honestly, gen 1 is still my favorite in terms of designs (though I think it's one of the worst in terms of games, I'd rather play FireRed/LeafGreen over the original games).

Just as something I noted right now, I think the thing about gen 1 was that it introduced this kind of world where common animals could be something more. It kind of gave real life this kind of magical undertone, like hey that mouse might be a rattata. Like, we were living in a world where maybe we were overlooking the common things we see every day. As the gens progressed I feel like pokemon became less about fantasy undertone. I feel like that's kind of a reason why pokemon go was so popular with gen 1 gamers, because it reintroduced that magic. The feel is just not the same in later pokemon generations.

I agree. Gen 1 pokemon designs are easily some of the worst. It's tied with gen 5 in that regard

Definitely not, Gen 5's are atrocious on the whole. Ice cream cones, garbage bags, goth kids, monkey stoners, roadkill fish, legendary genies? What the hell??? I'm still mind boggled all these years later that most of those designs ever saw the light of day. And that's not even mentioning all the ones that are literal ripoffs of the gen 1ers. Gen 2 and 4 have always been a tad on the forgettable side for me, even though they're not bad. 3 and 6 have the best designs by far in terms of quality and creativity, then I'd go with 1. Sure some of the ones the OP mentioned are pretty lame, but overall the simplicity of that gen was done very well and given just enough flair to avoid being boring in most cases. Pikachu is the perfect example of that, and most are more Pikachu than Ekans. They're memorable for a reason, because on the whole they're simple but well done.