Woah! Blast from my gaming past!
I used to play Crystal Quest on my Macintosh II back in 1988. Hours and hours. The computer was right next to my bed in college, so I could roll out of bed to play Crystal Quest. The little "boing" sounds, and the "aaah!" as you left the wave.
Well, it is now available on Xbox Live Arcade. I plunked down my 400 points (aka US$5) and bought the sucker. It has a revamped gameplay, along with the classic mode.
So retro... but way fun. Very recommended!