This is mid 90s, I remember playing it on a PC that didn’t even have Windows on it. It was an alien invasion side scroller. You’re some action dude that has to fight his way through the levels, some of the early enemies are little blobs that jump at you.
Any help appreciated :)
Edit: found it, it was Bio Menace! Thanks anyway for all the suggestions, folks :) Happy gaming!
Not Commander Keen, it was a lot grittier (if you can call games from that time gritty). Thanks though!