Classic gameplay that is still imitated today for a reason: it rocks.
Graphics: The game is vector-based black and white. Your ship is a white triangle. The asteroids are slightly deformed white circles. Your ship fires white dots at the asteroids. When your shield go up you turn from a white triangle into a white square (denoting "shields up" I presume). The asteroid field is 2-dimensional. In other words, the game has no graphics. At the time of its release, even Frogger and Pitfall had some color. Everything does move smoothly, though.
Sound: I am going to type the entire sound library phonetically for you: Blip, beep, boop, booop, squip, eep. Midi had not yet been developed.
Gameplay: Awesome. This game was the Mario Kart of its time in multiplayer. There's no end to the game, just a high score (and therefore bragging rights). Fast-paced, simple, clean, and fun. They're still making games based on asteroids today, albeit with updated graphics, because the gameplay is that timeless.
If you haven't played this game before go to a mall kiosk and buy one of the Atari joysticks that comes pre-loaded with this game, Missile Command, Centipede, and all the other greats. You owe it to yourself to play Asteroids.