I have the Linux version, iirc. I got it once in a Humble Bundle. Also there it seems it never got updated. It is basically playable but you may get a mess with the resolution on fullscreen startup (that I have to fix each time by siwtching to windowed mode and back to fullscreen) and the game definitely does have a few bugs, though they are relatively rare. E.g. I couldn't get one secret level to work at all and an early intermediate boss spawns rarely in a way where you can't reach it or it can't reach you and you have to restart.
The game has a very high difficulty (at least in my eyes) and it is very luck dependent (distribution of emenies, map randomization, powerups / mutations). I got past the ice world one or two times but no further.
I'd be happy if an up to date version was available anywhere. It sucks that Steam seems to receive all the updates and attention while paying DRM-free customers are left in the dark.
I got the Indiebox version of this game and the USB it came with did not have all of the files needed to work on Linux.
Indiebox got back to me but the fix they gave me - now has the game working but I am having the issue you are having. I log on here to see if others were having the same issue.
What a shame.