It's quite possible, if Microsoft keeps the Halo franchise almost synonymous with the Xbox franchise (in a good way, not a limiting way), that the premier Halo title for the next Xbox will see similar sales and a very high attach rate. For instance, I'm not a Halo fan at all, I'm not even really a big FPS fan (the last FPS I really got into was Quake 2, heh). I bought my 360 for Tales of Vesperia. Nonetheless, I picked up a copy of Halo 3 because it seemed wrong to have a 360 without that title. I don't know a single 360 owner without Halo 3.
Although, unless Halo: Reach blows everyone away and overtakes Ocarina of Time on metacritic and such, I think the only titles that could rival or beat Halo 3's sales would be a Halo 4, Halo 5, etc.










