I love WACKO! It's a pretty simple concept, but fairly addicting. You can actually play just fine with two hands.. one to more your ship around with the trackball, and one to fire with either joystick (you choose, based on your handedness). It's actually quite playable on most mame cabs that people are building, what with the proximity of trackballs and joysticks.
I also love the look of the cabinet--so many slants all over the place! Quite original.
Later,
88mph