Sound - The sound is that of the defender (you) shooting at the invading aliens and the music is when you kill the aliens. Not really much to comment on but some classic Atari 2600 at its best.
Graphics - the attacking aliens look great, even though they can be compared to the aliens of that of Space Invaders. The wall itself looks more like a simplistic maze although you can only move around the outer part and move in when you have failed to protect the wall and the outer most is destroyed.
Control - make sure your 2600 joystick is in good condition, as you need free and fast movement around the wall to combat the invading aliens. Other than this timing for shooting is crucial as aliens appear at different angles, not just centered.
Playability - this is a highly playable game as it offers a different perspective to the "alien attack" which is a popular formula for the 2600. The controls are smooth if your 2600 hardware is good, and reaching that score of 999,999 (the highest the game will go), would bring a sense of worth. (I haven't personally reached that yet), but I know it would.
Overall rating - I rate this game as 95% as it offers a unique perspective to "aliens attacking" and is extremely fun to play.