In it's original 1980's arcade format, this was one of the most fun games out there.  Well, at least for me, because it was the only one which I could consistently get the high score.  Well, that and the fact that it's vector graphics were very crisp for the time.  The trouble of course is that Tempest's main controller was a spinning knob, making it very difficult to replicate the play on a PC or console.  If you have ever played it you'll know precisely what I am talking about, it's just not the same without it.  If you haven't played the game, you're in luck, even without the spinner, you can still get the idea via this Atari online flash game which absolutely nails the sounds and graphics.