I'm even quite sure why, but I really liked it.
First off, it's challenging, sure, but not even close to unwinable. Though *I* certainly wouldn't have had the patience if it wasn't for the password based resume option. (Nice choice of passwords, by the way.)
I liked weapon selection (the Charged Ion Launcher ROCKS), though it might have been nice if the turrets were outfited with various weapons too.
I did find the controls a bit annoying at times. Some of that must intended I guess, (low-G and all), but why for example does pressing Up when the anti-grav suit is uncharged cause you to stop moving forwards? It seems like it should just do nothing. It also took me a while to realise that pressing down to fall faster used up the (anti?)grav suit's charge as well. That one's perfectly reasonable, but until I figured it out it also contributed to frustration with the controls too.