Tested on a Late-2006 MacBook Pro with 128 MB RM X1600 graphics, and 10.6.5/CXG 9.2.
The game works - well, for the most part. At low resolutions/bit depths, there were some moderate graphical glitches, namely thinly faint lines running horizontally across the screen, and the top part of the screen flashing whenever there was a significantly high amount of gibs from dead aliens on screen.
At high resolutions, the game slowed to a crawl. The happy medium seems to me 1024 x 768 @ 16 bit graphics with graphical detail set to low. The lines are still there, but the screen flashing is much less frequent, and the game plays quickly.
All in all, a worthwhile game for $6. I'd just like to know why it's called "Alien Shooter" when most (all?) of the monsters are cooked up in a lab.