OK, I guess I'll post the first little review here:
I wasn't one of the diehard fans that lined up outside BestBuy @ midnight or anything - I preordered my copy during some promotion so I got the limited edition for only $38shipped [the metal case is friggin' cool]. I was hyped about the game, but not to the point of rioting or anything...
The first session I had with it was story coop mode. This was one of my favorite features of the first one, and I was expecting this version to be even better. I was overall unimpressed. Dual-weilding is really cool the first time you realize you can do it, but the initial charm wears off kinda quick. This one doesn't feel any smoother control-wise (not that it's bad by any means, just not any better). The ingame graphics are great, but the cutscene graphics are very hit-or-miss - some scenes look terriffic, while others look like shite (master chief and all the bad guys look great and are animated well, but all the humans look like stiff, boxy crap.) The framerate was pretty crappy for coop - worse, I felt, than the original.
I know so far it sounds pretty negative, but alot of the criticism is kinda nitpicky, primarily because this the release of this game to some people has been regarded as highly as the second coming of Christ

, and I just want to point out that there's plenty to keep this game from being perfect. Some of the POSITIVE things about this game - the enemies seem smarter now, along with your supporting teammates. The enemies are harder to take down too, which makes the challenge a little better. Alot more opportunities to commandeer vehicles (which you can now do via a very cool, very addictive 'jack move'). The weapons have been balanced better (the needler rawks now), along with some pretty cool new weapon additions. The energy sword owns all.
Finally, the mode that everyone was clamoring for, XBox Live. I signed on shorly after playing around with the Coop mode. Takes several minutes to load up a quickmatch (it does all kinds of number crunching to determine the best possible match for you, based on level/skill rating, ping, etc.) Kind of annoying when you're impatient to shoot someone in the face (same gripe I have with the 3day gun purchase waiting period...). It finally loaded me up into a map, and the framerate/lag was HORRIBLE. I honestly couldn't even play it. I signed off after just a couple of minutes in disgust. The next day, however, I decided to give it another go, and I must say, it ran as smooth as silk. I think the servers were just totally capped out the first day - checking bungie.net showed me that there were over 50,000 people playing at the time, so I guess it's pretty understandable. On the topic of bungie.net - they've done an awesome job there - you can type in your (or anyone's) gamertag, and get their ratings, how many games they've played, even a listing of the last couple matches and their stats/outcomes.
In conclusion, I recommend picking up Halo 2 if you liked the first one, and especially if you play on XBox live. Not the greatest game to ever grace the earth though; if you want a great deep, all emcompassing game, check out GTA:San Andreas. If console FPS's are your thing, Halo 2 fits the bill well.