THE LIBRARY I wouldnt say its the toughest board, but it is most defintely the most annoying. Its like your running around in circles the whole game. Its especially a pain when you play it in Legendary, so much flood. Trick is shotgun and rocket launchers with grenades. Thats all you need for that board. After that board you still have another 4 levels to go I believe. You end up playing the previous levels you played backwards. Its pretty cool, but no you werent near the end yet.