I played through the first Halo and really enjoyed the single-player campaign. I never played the multiplayer game until I bought Halo 2.
Let's get this out of the way first: Halo 2's multiplayer is unparalleled. With a multitude of multiplayer games (Capture the Flag, Juggernaut, Team vs. Team, etc.) and a dizzying variety of terrains, there's plenty to keep Halo fans busy blowing each other up. The addition of the alien Elites as a playable character spice things up. You can also wield two weapons at a time, one in each fist, providing another combat option for those gunslingers that like their battles John Woo-style.
Unfortunately, Halo 2's single-player campaign is not as impressive. To whit, the alien Covenant's entire society is based on the idea that activating the giant rings throughout the universe (known as Halos) will put them on their journey of spiritual evolution. The reality is that Halo is a weapon designed to destroy the Flood, an infestation of aliens who turn human and alien alike into vicious zombies. And how do you keep the Flood from infecting every living thing? Why, by utterly destroying every living thing in the universe of course!
Play alternates between Master Chief and the alien elite known as the Arbiter. This gives the player both sides of the story, which is interesting…to a point. Eventually, the plot converges enough so that the two characters should really end up fighting each other. That would have been something, if the AI made you play through both battles from opposite sides by creating an enemy that uses your own moves.
But instead, about midway through the battle for the universe, a giant plant that looks like Audrey II from Little Shop of Horrors shows up. This planet, speaking in Jabba-esque guttural tones, rams the plot down our throats by grabbing the Arbiter and Master Chief and shoving them into opposite plot lines: the Arbiter ends up working with the humans, Master Chief ends up doing the alien dirty work.
Then things really get going, and just as Halo 2 hurtles towards the final battle on Earth…the game ends. I should have guessed something was up when, during E3 interviews about Halo 3, the CEO of Bungee only had this to say: "Are you ready to finish the war?" What he meant was, "Are you ready to finish the game you thought you were finishing in Halo 2?"
As you've probably noticed from my review of the second installment of Pirates of the Caribbean, I really, really, REALLY hate movies and games that fail to provide a whole story. It doesn't matter that this is part two of a three-part series. Writers and developers have an obligation to provide a full story; you CAN create a story with a beginning and end even though it's the middle of a series, as evidenced by The Two Towers.
Halo 2 is an improvement on the original, but it loses points for a weak campaign that forces you to play both sides, then throws in a talking plant to clean up the mess.