Wow. The graphics and sound are amazing. I've played for a couple hours now and it's definitely an excellent game. I was a bit surprised at one of the game twists, but I won't spoil it for you.
The new weapons are cool and so are the vehicles. They've made some changes to the Warthog and the tank (what is it called?), but I think they're good changes. The Marines in the game are a bit smarter now, employing the rocket launcher and some of the other heavier weapons.
The between level cinematics are pretty cool and the story line is cool enough that I don't mind waiting for the next level to start.
More later.