THE MAW (Halo)
You had finally beaten those dreaded flood levels and were on your final race to victory. Your only mission left was to destroy the Pillar of Autumn and Halo along with it. The Warthog speeds through the facility as you get shot at by everything the game can throw at you. You pay no attention to the pesky alien foot-soldiers as you make your escape, narrowly missing building columns as the structure begins to collapse. The level may not hold up quite as well in comparison to the games available today, but back in 2001, this was cutting edge and unbelievably tense. There was great satisfaction in being able to mow over all of those pesky aliens with the Warthog as the facility begins to destruct around you.
It was chaos at its best, and it was punctuated by a six-minute countdown clock that you were racing against to make your great escape. Level designs like this were a huge sign that games would never be the same again. Given how major a franchise Halo has become, its hard to remember a time when Halo: Combat Evolved was a dark horse that nobody expected. A launch game for the original Xbox, and one of the greatest launch titles ever released.
