I am pretty sure, there won't be another HD-Game to sell as much as Halo3 on one single platform.
Right now, Halo3 is at 9 million. With the release of ODST and a possible Halo3 + ODST bundle, sales will reach 11 million quite easily. ODST might move more Halo3 units.
The toughest competition will be GT5. The best selling game of the series sold almost 15 million units. That is a lot. But the install base for the PS3 is much smaller than it was back in the days for the PS2.
Final Fantasy XIII will have great software sales, but because of the fact that the game will be on the Xbox360, the sales will split. Furhermore, the best selling FF game sold almost 10 million.
I can't think of another game to come close to 11 million. Is there a great franchise I don't remember right now?
What do you think?
Imagine not having GamePass on your console...
