A big emphasis on Halo is the idea of balance. You can't chuck in a super bomb or something without thinking about it. You'll completely trash the game play.

When you break it down, see the detailing in the maps, see the creative thought that goes into the layouts, it's quite amazing.

I'm sure they'll add new modes of play. Toss in a new feature like that, you've completely thrown all previous strategy out the door and will have to work on a new one. (As a player that is)