Just finished the single player in Halo 2, so I feel like I can talk about the game in more detail.
The single player campaign improves on the first game in almost every way. For example, in the first Halo, there was a load screen for every large chapter of the game, but then none within each level until you got to the end. In Halo 2, there is a load screen when you start the game but then there isn’t another one until you quit. Ever. Whoever implemented this gets super genius kudos.
At first, the enemies seem a bit too easy on the Normal difficulty level. While they seem to fall down easier, they also seem faster and meaner than in the first game. The new enemies are mostly enjoyable. By the end of the game, they were beating me up pretty well. I like the energy sword, and I like the shotgun. Dual wielding the plasma rifle is also useful.
The plot twists and turns much like the first one, but overall the pacing is much better. The stages were more linear, with no backtracking and fewer sequences of dozens of identical hallways to get lost in. There are multiple moments in the game where the action is so frantic that you will want to cower under the couch and sob like a little girl.
The ending is a bit abrupt, and hints at a sequel much more explicitly than the first game does. But the final stage is much less annoying than “the drive the warthog off the end of the earth” deathmarch that ended Halo 1.
People have complained that the game is short. These people are nuts. What they mean is, the game’s pacing was not padded out with worthless backtracking missions and boring driving.
Not so good:
There were some rendering glitches in my game, especially in the in-engine cut scenes. What would happen is that textures, or sometimes whole objects would just pop in from nowhere after a scene change. These were relatively rare.
Checkpoints still suck. But there were only one or two sequences between checkpoints that were so long as to piss me off. Usually, these took the form of “you must kill these 10 things over and over again because you keep dying on the 9th one”.
I still hate the Warthog, but the power sliding makes it less stupid.
Too many of the weapons are basically useless. Or maybe I’m just useless trying to wield them.
The multiplay rocks. I don’t think much more needs to be said about it. My only gripe is that the respawn times don’t give my hands enough time to rest between rounds.