Basically, the screen is set up like this: The base you need to destroy is on the right side of the screen and is protected by a shield. You need to chip away at the shield with your missiles, or you can "eat away" at the shielf by continually touching it with your ship. However, a relentless missile will chase after you, and the base frequently turns into a swirling projectile that shoots your way, so you need be constantly moving. There's a rainbow colored stripe in the center of the screen. While you're in the stripe, you can't be harmed, but you can't fire either. To destroy the base, you need to use the Zorlon Cannon, which is activated by eating the shield or touching the base. Once the cannon appears, you need to fire it at the base, but make sure you get out of the way so that you don't get killed. If you make contact with the base, it's destroyed and you can move to the next level. There are eight variations, including a two player modes, a bouncing Zorlon Cannon, an easy version, and Ultimate Yars!
The graphics are very good. The rainbow stripe is vivid and constantly changes colors. And when you destroy the base, an explosion of colors emerges and then compresses to the center of the screen -- it's definitely a sight to behold. There is, however, the inevitable flickering although it's not as pronounced as in, say, Defender or Pac-Man. Sound effects are minimal, but what's there seems to fit in with the game's sci-fi theme.
All in all, Howard Scott Warshaw (the game's designer) did an excellent job salvaging a failed Star Castle game into one of the best VCS games ever. You can't help but wonder how this same person could do Raiders of the Lost Ark and E.T, but that's another story.