Metisse is made of a modified version of fvwm and a special X server called Xmetisse on top of Xorg.
You can see that in a terminal window (assuming you have only one graphical session running):
$ DISPLAY=:0 glxgears
should give you very different results. (try: echo $DISPLAY; you'll see it is not ":0" in Metisse)
It is normal (in its current experimental state) that Metisse cannot run 3D-related software. You can still run those applications as above with "DISPLAY=:0 " before the command, but then the window that opens doesn't have borders because there's no window manager on display :0.
I didn't know for the screen shots; maybe it is related...