>>13242046I think there are probably multiple factors. For one thing it introduced Stealth Rock. Granted, entry hazards were already a thing, but Stealth rock changed everything and the Gen 4 metagame lived and died by its rocks. This caused many otherwise beloved pokemon to fall out of favor.
Another factor is that the designs were rather busy. You can see it in the OP picture. Arceus, Giratina, Palkia and Dialga are the most complicated-looking legendaries. That busy design ethic runs through Gen 4 quite a bit and it bothered many people. Notice that when Gen 5 rolled around they simplified and cleaned up the designs of the new pokemon a LOT. Compare Reshiram and Zekrom to Palkia and Dialga and you can see the difference. (Not to say Gen V is perfect. It's simply a step away from the busier Gen 4 design ethic)
The slowness is also an issue, although it was fixed in Platinum (As were a lot of things), another thing people liked in Gen V was how FAST battles went. The HP bar scrolled faster, the textboxes didn't linger forever, and overall it was a much faster-running game. That counts for a lot.
Also, one thing that WASN'T fixed in Gen V was FUCKING FIRE/FIGHTING STARTER AGAIN?
Anyone else, feel free to pile on other things that bothered you about Gen IV
