Apparantly liking good designs makes people genwunners and a fan of generic designs.
People need to like crazy new designs now because anything that's not zany is boring or something.
I'll break down this fallacy by categorizing the readily criticized pokemon.
Based on animals type
Ok so most gen 1 pokemon are based on animals but some closely resemble them like Pidgey, Ratata, Seel, etc. It's like ok this is a problem for some reason. This doesn't make them bad designs they just happen to be based off real life animals. Would you say a bird is badly designed for looking like a bird?
Articial type
Here we get Grimer, Muk, Ditto and Polygon
Again all heavily criticized but what do you expect mutant sludge to look like? Like you can't expect this intricate sludge dragon for a pokemon that's meant to just be pollution, Ditto is a failed clone of mew so again pretty creative being able to transform into any pokemon, and Polygon is exactly what you'd expect a prototype pokemon to look like. These designs make sense if they wanted to be more creative they could but it would make no sense lore wise.
Object type
Finally we get the Magneton and Voltorb's of the group. Voltorb is cool because he's the inspiration for the pokeball and magneton is known for being used by humans to discover the workings of electricity. To us it's boring because we all know what a magnet and pokeball is but these pokemon existed before any of those were a thing so it makes no sense to say it looks like a pokeball when a pokeball is meant to resemble voltorb... again not bad designs just people having logic fallacies.