Without theater mode I would have never realised how good I truly was. Also when you have that question of how did that guy kill me. You can watch as he slowly walks behind you. Also its fun watching movies of drive by zombie shooting.

Has anyone played a game that had this level of control? I mean the camera can be complete detached from the action and is basically free in space to go pretty much anywhere and look at anything. I know replay has been done many ways but this is the first I've seen with this level of control and detail.

This is the first game with complete freedom

No, I don't think so, the level of detail and freedom is awe inspiring.

 You've got .mvd files in QuakeWorld. You also can view all players first person view there.

I have yet to play a forge game where you edit the game while playing.  Thats the most innovative thing about halo 3 imo.

No, nothing has been done to this level before. I noticed the detail especially in the desert level where you zoom the camera in on the individual grains of sand.
Another game with a cool free moving camera is motorstorm-
although extremely limited, You can pause the game at any time and pan and zoom as you wish. This is especially cool because of all of the small bits and pieces of the crashing cars exploding in HD glory.
BUT as I said- nothing compares to the freedom of the system in Halo.