As is OpenGL from what I've heard.
Both will strengthen AOS4 against the competition.
Gallium3D is part of Mesa, which is the premier open-source OpenGL implementation. You wouldn't get Gallium3D without Mesa, they're part of the same package (AROS has it too).
One point that's worth mentioning is that some of the newer features of OpenGL haven't been implemented in Mesa yet due to license restrictions, which is a bit of a shame. In any case, Mesa is a lot more complete than OS4's current OpenGL implementation.
