Halo 2 is what a sequel should do and expand upon the first game. We not only new types of enemies and weapons and different locations but also we get to play as the Arbiter. We get to play as the enemy! In the main campaign! Arbiter is an interesting character who goes through an arc about rebeling against the covenant and freeing his people. Along the way he has the ship commander Rtas by his side.
The villain, prophet of truth, is a manipulating bastard who is so cunning. Basically a religious antagonist who will throw a species under the bus just to gain control of the covenant. By his side is the brute general Tartarus, whose a dick to the elite race, and super satisfying to kill. Even if he was just as brainwashed by the prophets.
Overall the story of Halo 2 is great. I have even talked about the humans or the main character master chief! But yeah Halo 2 is great. Now it's time to finish the fight.