Hello,
have you try out playing Glest without Compiz or Beryl?
Perhpaps Xgl, Compiz or Beryl and 3D Games
doesn't like play well together.
I play Glest with FreeBSD, but without Xgl, Compiz or Beryl.
But i have OpenSUSE installed to,
(but don't use it really)
with Beryl, 3D Games have Blank Screens
or only some Game Parts viewable, with Beryl active.
Perhaps you can switch of Beryl,
i see the Beryl Manager on your Screenshot.
Greeting, Fusselbär