Science fiction film fans will remember when miniaturised doctors were injected into the bloodstream of a human to operate on a brain tumour. Here, you've got to destroy the nerve centre in Zyco's brain. an indestructable (their spelling) alien before your miniaturising pill wears off, avoiding blood corpuscles and antibodies. There is illogicality to this twist on the original. Why does the alien permit injection? And why wouldn't a human body, exploding full-size in his brain, finish him off anyway?
Screen display also shows lack of research. Basically. a visible maze in the convoluted shape of a brain with some circles (corpuscles?) whizzing around, and a spiderish shape I assume to to be the target at the centre. Your weapon fires only in the direction you are going, without effect on corpuscles. Controls are extremely sensitive and touching anything changes you from a tiny dot to a mountaineer in Lederhosen. and sends you back to start again.
And that's it. Possibilities - lungs, heart. variety of opponent - must be left to a future programmer with more imagination. Illogicality aside, won't interest for more than five minutes.