Halo, as a franchise, is a machine. It could be argued that Halo kept the original XBOX as a viable console and justified the launching of the 360. The ripple effect from those two facts alone have changed the console market as we know it today. Additionally, the sales of Halo 3, on a much smaller install base, rival the sales of multi-platform games that (with combined install bases) had double the potential customers.
Do I agree it is quite the force that Ballmer says it is? Maybe not, but there is some merit to it.
Now regarding the emotional impact....well I think that is too personal too compare, especially when confounded by system loyalty. That is, Star Wars and Harry Potter are movies that can be seen and enjoyed by just about anyone. Halo, is limited to XBOX/360 owners, so obviously PS3, Wii fans would not feel as invested in the franchise.
Essay Pro