1. Better graphics
2. Better multiplayer
3. Plot ending and/or twist to keep it open for when Bungie decides to go back
4. Even more customizations
5. Playable Flood
(Yes, those did take me hours to research)
Yet, probably the most defining change in Halo 3 will be
After all, what made Halo 2 such a big improvement? Sure the pretty graphics were nice, but what people really wanted was more death and destruction. With the possibility of three weapons at a time equals more fun. Sure they will have to add that into the plot somehow, such as a Flood bit Master Chief so he grew another limb...but hey, who wouldn't want another arm?
7. Master Chief will finally take off his helmet...so we can see his face! Then people will be crushed that Master Chief is actually another butchy woman like Samus.
Wow, what would cheap people do without MS Paint? Anyways, an official source, my 12-year old Halo crazy cousin, is that Halo 3 comes out next summer, so stick with Halo 2 until then. I've beaten it 14 times now.
Additional facts: If you didn't get the joke in my Femmy Master Chief picture, then you are not a true fan of Halo.