The receeding target circles, as seen here with a bit of photoshop enhancement, are an interesting way to keep shots more accurate at greater distances. Most third person action games do not cover such a large environment so a system like this was never needed. Games that came to mind were Shiny's MDK and upcoming Messiah. I think this is pretty ingenious myself.

In the figure below you can see the new targeting system built onto the HK G-36 and in some ways it mirrors the proposed Halo system.

Image from the HK Pro website.

At this point, although I do imagine some refinements and additions, I am very confident that Halo does not need to be a first person game. I also noticed in the movie the top right hand "HUD" which went from green to red as the Marine fired off his assault rifle in the day 3 footage. Clip management should be very interesting. An especially nice touch would be webgear or something equivalent that becomes depleted as you burn through all of your munitions. I wonder how they'll handle reloads on the minigun?