Here are some Advantages and disadvantages of using Halo and/or Halo 2 as a game engine to use for machinima.
Great actor ability, the multiplayer allows for a lot of characters to have in a video (Up to 15 if only 1 camera man).
Good virtual camera the HUD is pretty easy to remove and there are tricks to get rid of your gun.
It doesn't allow full involvement of everything. While it does allow easy set up, not everything is good. The head bobbing can be a pain if not done right. And since most people film over X-box Live (XBL), it lags the head so that it cuts out frames. This is right in the code of XBL so that people produce less lag by sending less frames out to the clients. In doing so, it renders online use of the head bobbing not use-able.
It's also very over used. Since Template:Red vs Blue came out, many people have decided to rip from the fame of them. And about 99% of all fail due to A) lack of interest and/or B) Lack of a decent crew.