While I don’t quite agree that it warrants a WORST GAME YOU’VE PLAYED title, I do think that the Halo 2 campaign was clearly rushed in terms of its development, and that its quality suffered as a result.
There are some parts of the campaign and plot, especially toward the end, that are clearly unfinished or just flat out stupid.
It starts off great, and then it just gets worse, and worse, and worse… subtly, but then you compare the beginning and the end, and you see the huge difference in quality. Obviously Bungie ran out of time toward the end of the project, so they initiated crunch mode, scrapped half the game, and rushed it out the door to meet the ship deadline. They even admitted to doing exactly that in numerous interviews and other documented sources.
As for it being hard, yeah it’s probably the hardest Halo in the series, just for the sake of being mind-numbingly difficult (aka there’s no good reason for it to be that hard).
I still liked the game though. :3