Halo CE had the best story line and began the craze for Halo. It also introduced the world to online FPS. Halo 2 took it to the next level in terms of weapons, vehicles and graphics. But it's story was lacking. Halo 3 had better engines, weapons, and storyline. But it never achieved the fame of CE. ODST introduced Firefight, which made multiplayer much more fun. Reach represents the culmination of the games into one masterpiece. But once again CE takes the cake.