Ah, yes...and be sure to try the Hack INVADER X. Altough the Graphics are not as good as in the original Game, it plays a bit faster!
When I first played it, I found it somehow boring: It seemed very simple even for an Atari 2600-Game, but playing it again a while later, it really hooked me: Of course, the Gameplay is still very simple, but the Variations of the Demons keeps it interesting and you want to see what comes next. Guided Shots ("Tracers") and other Options give Variations to the Game, I didn't recognize when played by me the first Time.
It's a Classic and a great Game for Hiscore-Hunting. And if you think, it's repetetive, like me in the first Rounds, give it another Try - it may surprise you!
This, along with River Raid, are two of the best shooters for the 2600. Rob Fulop was really good at shooters (2600 Missile Command, 8bit Space Invaders, etc) and this shows his skills at their best.