I think Forza 3 and PGR 4 basically proved that the two-year sequel cycle doesn't really work for racing games. Hopefully Microsoft will figure this out and give Turn 10 the appropriate time to come up with something a little more innovative, and not just kill the franchise (which is, IMHO, quite excellent).
On the plus side, it'll make an _excellent_ pack-in the next time they decide to go that route.
On the plus side, it'll make an _excellent_ pack-in the next time they decide to go that route.