Much hyped, but is it worth it? Sort of.
Halo 2, while still a great game, suffers in that the multiplayer simply isn't as good as the original Halo's, despite the addition of online gameplay.
Gameplay: Halo 2 takes the original Halo's gameplay, and adds the ability to dual-wield weapons. This comes at the expense of being able to throw a grenade. This can lead to gameplay imbalances, though system updates have helped remedy the situation. The most glaring weapon imbalance is the sword, which will make you stop playing on XBOX live, the rocket launcher is pretty bad as well. Simply put, both are far too powerful for the amount of skill they require.
The single player is better than the original's in that the levels are more varied, and don't all look the same. The story is disappointing though, and the game is a little on the short side. It's still fun to play though.
Graphics: Nothing to complain about here, probably the best on the system, along with Ninja Gaiden.
Sound: Great soundtrack, but why no music in multiplayer?
Value: The multiplayer, while flawed, is good enough to play many games with your friends. However, you'll probably have more fun with the original Halo. As for online, it's pretty fun, but expect to get frustrated after a while. Once you get up to a certain level it's fine, but the first 15 levels or so can be miserable, definitely hit the mute button.