To clarify my earlier comment, I think Halo: Reach will be the biggest 2010-game. Meaning, biggest out of the ones releasing in 2010. I think Wii Sports Resort and New Super Mario Bros. Wii will sell better during 2010, but they are 2009-games. So yeah, they'll be bigger in 2010, but I think that Halo: Reach will be the biggest 2010-game.
Hope that cleared stuff up.
(The only game I see realistically having a shot at beating Halo: Reach is GT5, but I think Halo: Reach is esentially Halo 4 so I see it easily going to 8 million ... Something I don't quite see for GT5. Sorry!)









