The best parts: Epic sci-fi campaign; overwhelmingly addictive multiplayer; larger than life heroes; smart enemies; imaginative weapons and vehicles; expansive environments; simple yet sophisticated combat.
The WORST part: THE FLOOD
The first two-thirds of the original Halo are a revelation. After years of being trapped in dark, linear passages, fighting endless swarms of repetitive enemies with uninspired weaponry, we were finally set free.
Now, we had beaches, mountains, valleys and soaring alien towers to run and leap across. Now, we had jeeps, tanks, helicopters and extraterrestrial hovercraft with which to cover vast swaths of ground and sky. Now, we had a diverse set of enemies who could not only think and talk, but almost inspire sympathy at times. Now, we had crazily inventive guns shooting ammunition in all the colors of the rainbow.
The Flood are the antithesis of everything that is new and unique about Halo. Unsurprisingly, they're also responsible for the absolute worst levels in the trilogy's history - "The Library" in Halo 1 and "Cortana" in Halo 3. Pure torture.
Dishonorable mention: We thought about choosing the Halo games' endings for this section, but then thought, "What endings?"