I took about 2 days off from my 70-page paper due on Monday in order to waste my life in an orgy of Halo 2ness. Since obviously most of my 10 readers have not made up their mind on the Halo 2 issue already, I will post my preliminary thoughts.
The game is basically a good sequel. The designers were probably thinking "Okay, let's take everything about the original Halo and make it a little bit different and a little bit bigger!" So there's a few more weapons. You can use the older weapons differently. The single-player campaign so far appears to be a direct mirror of the original Halo's campaign, without the surprises, though it is a bit of a shock to play as the Covenant (though I'll be able to tell you more next week.) Which is ironic, because the second half of the original Halo's campaign was a literal mirror of the first Halo's campaign.
Multiplayer is where it's at, though, and things have changed, not necessarily for the better. What made the original Halo such a hit, I think, was the way that you could play it happily with 3 other people on the same TV. Half of the maps were playable by 4 people, and 6 was just about optimal. In Halo 2, there are two maps that are sized for four people, and one of them is a clone of an old map. Obviously, the game was designed for online play. Online play is fun and all, and it'll make the game a lasting hit, but I doubt it will bring the sheer joy as actually having the people in the same room as you.*
Still, it might be enough to get me to get an Xbox again. Sigh
*minus the smell, which may be important.