Continued the game, and beat the Library. I can see why people complain about it, but I found it more long, tedious and repetitive than difficult as such. Beat the following level as well, which was a bit more interesting although it was covering a lot of ground I'd already seen before. Was nice to ride a Banshee, but boy do the vehicle controls suck!
It's getting a little better, but only 2 missions to go until I can move onto the superior Halo 2.