Agreed on the zen mode. It's why this game is one of my all-time favorites. I like how you have to avoid not only the enemies but also being hypnotized by the excessive amounts of rainbow strobing lights.
This is my all time favorite game too!!! The only one I really want to play ever, I played it when I was on acid once in 2000. I know exactly what you mean too scrungus-- about that full zen mode.
Eugene Jarvis (author of Robotron 2084) https://en.wikipedia.org/wiki/Eugene_Jarvis
I first played Defender as a small child and 'Target: Terror' is the most recent. Some great arcade action and satire among these (Come on, NARC and Smash TV are in there).