This is all about graphics, not visuals, so only discuss the most technologically impressive games of the generation. So no DS games, because PSP had objectively better games in terms of technology. No 3DS games because Vita. Talking of Switch games mention the best looking game in portable form and not on docked.
I'm doing this to keep bias out of the way. Obviously many would say a DS and 3DS game because it "appeals" more to them visually which mocks the point of the discussion. Its appreciating technology, not art styles.
Sure, but technologically impressive can also mean it's impressive for the hardware it's on.
As an example, Resident Evil: Revelations looks incredible on the 3DS and I still have a bit of a hard time believing it runs on it.
I'll think of more later, but yeah, there's definitely more impressive GBA picks than Pokémon lol. I recall seeing a 3D game on it once, it was quite ugly of course but it was proper 3D. Can't remember the name.