1UP has an interview with Tyson "Ferrex" Green about Halo 2, including his involvement in The Library level from the original game, and the tongue-in-cheek homage to it in Halo 2:

The Library was actually the first mission I was put on when I came here. But the thing that keeps me sane at night is that the library was mostly designed when I got here, so I don't blame myself for that.

Early in development I wanted to...I've got this cross to bear, a desire to say, hey, all you guys making fun of me, I'm gonna poke back. The idea is that we're sort of paying homage, and also being a little self-conscious. We recognize that [the Library] wasn't the best level ever, we're conscious of the mistake that we made. But [I wanted to address it] not just where I say that in an interview, but in a way that shows, hey, look, here's the ghost of our past, we're not going to hide, we're looking back, and it's not a grueling level like the Library was.

Thanks VoodooExtreme.