Halo fans were already moved into XB360, if they hadn't one yet, by Halo3. Look at the charts, Halo3 gave a bump so big to even eat some of successive Xmas sales, a lot of people otherwise wanting an XB360 for Xmas simply couldn't wait. It's quite safe to guess most Halo fans already have an XB360 by now, also because this console has offered the cheapest current gen model available for a while. Nevertheless I think a bump can happen, it's a big game that adds to the already wide choice XB360 already has.