Hey thanks for the nice comments! Defender was definitely an influence when I built this (with a bit of Jet Pac and Choplifter thrown in!)
Thanks for the bug reports. Will check out human attractor function and try and tweak things a bit. I have hopefully fixed the other bugs you mentioned (new download is now available).
Level 4 bug. If you pick up all the humans and destroy the boss that should finish the level. If you don't pick them all up then you fail.
"I" bug. The "I" is actually an "!" but it looks like an "I" with the font I am using. Fixed.
Thanks again!