Why Do People Rag on Perfect Dark's Single Player?

Although the multiplayer is arguably the biggest selling point for both GoldenEye and Perfect Dark, they both had very well put together and inspired single player modes as well. But for some reason, Perfect Dark's otherwise excellent single player is ragged on quite a lot by insipid GoldenEye purists. How come?

Slightly incoherent storyline and cheesy voice acting aside, I found nothing really wrong with Perfect Dark's single player missions; the only single player mission that I found mediocre per se was the one set on the Pellagic II. But apart from that the mission objectives were solid, the level art direction was up to scratch and the bad guy AI was improved a lot. I find it pathetic that a game is discredited on the grounds of a somewhat weak storyline when the rest of the game was highly polished and put together very well. And viewed objectively, GoldenEye's storyline was not so great on hindsight and was merely a near direct adaptation of a fairly average Bond movie.