What needs further clarification? I enjoy Gen 1's unique mechanics, like speed-based crits, full stat exp. allocation, connectivity to Stadium 1, Razor Leaf and Slash being stupid moves, Hyper Beam actually being a functional move, Wrap + Toxic being hilariously oppressive, Psychic being so busted that it actually makes Mewtwo as strong as advertised...
Meanwhile, what I do not enjoy about Gen 3 are Grass-types being objectively worse than Gen 1, which makes using Venusaur miserable, the IV/EV system, which I hate to this day, having to reset a ton of catches because of bad natures, mixed attackers feeling less optimal because of the aforementioned IV/EV system, and yet it doesn't have the Physical-Special Split we're used to, so it's the worst of both worlds, the Sevii Islands, not being able to use an Espeon without modding the game despite the fact it exists in the code unlike in Gen 1, Brock being even worse designed now that he gets a Rock move, the improved graphics exposing how plain Kanto looks, and Lostelle. Especially Lostelle.
In my opinion, Gen 1 offers an unique experience that is janky af, sure, but it's very different from modern games. For the sake of completeness, I think the same of Gen 2. Both are very different from modern standards and are tied to the GOAT side series, Stadium.
Gen 3 is closer to modern standards, but in that awkward phase of it where it just feels like a worse version of what we got today. Which makes sense as it was the first step towards said standard, so of course, there was a lot ironed out since then.
Any further questions?