While the single player campaign can be fun, that's not what keeps me playing Halo. It's the multiplayer over Xbox Live. Playing with gruesome, Titus, Tidus, S2 AM, glory, sue, steve, hurt, and the rest is what makes it so much damn fun. And if I were to download an emulator and an illegal copy of one of the Halos, then I wouldn't be able to connect to Xbox Live, and what would be the point?