"5 Bucks says you can't beat the Library level on Legendary (campaign mission from Halo Combat Evolved)" u say
I have done it already(shame I cant prove it to you since I cant sent u a screenshot cuz my laptop, where my halo combat evolved was, broke), it is raging and pain, every checkpoint feels awesome but you will eventually get thru the level, just avoid the flood as much as u can, and in the last part of the level, just run thru them, just straight to the index. Btw in reach, I only have 2 levels to go on legendary :)
WHOLEASS
Have you played the Beta for BATTLEFIELD 3? If you haven't, I recommend getting it (it's for Xbox 360 and PS3). I don't have the full game yet, but chances are it's going to be great and have a great replay value. I have BF: Bad Company and that was amazing. If that was amazing, this is probably gonna be amazing too.