Got it on Friday afternoon, as of Sunday, I had completed the entire campaign. My son finished it on Saturday. Of course, I don't spend hours on end playing it so I imagine others had it beaten the first day they had it.
Still, it was enough of a challenge that I enjoyed the game. The graphics are excellent and I can imagine what they would look like in HD.
Bungie also has a sense of humor. For example, they have added something called Forge. This basically allows you to pick a map and set up your own level for custom games. You can add weapons, vehicles, spawn points etc.
My son and I were fooling around with that on the weekend and on the sand level, sorry, getting old and my memory has dropped the official title, but anyway, there are two huge troop and vehicle carrying monsters called Elephants. They are slow as all heck but that's not the humor part.
We strategically placed fusion cores under one side and, using rocket launchers for that extra kick, we exploded the cores causing the Elephant to flip in its side. Now if you know Halo, you know that you can press a button on your controller, X in Halo 2 and RB in Halo 3, to flip the vehicle upright again.
Try this with the above mentioned procedure and you receive the message;
Press RB to flip.....wait, What? How did you do that?
Or something to that effect, my memory again. But you get the idea. Apparently you shouldn't be able to flip this vehicle?
Try it, have some fun. See if you can find other little tidbits like that.
Oh yeah, they also fixed the issue with getting outside the barrier on the games and using that to your advantage in a game. Go outside the barrier and there are different kinds of weapon systems or safeguards that will kill you. I suppose that's one way to stop people from utilizing glitches in the game.