First off, my computer assured me I was downloading a virus, but let me say it now: this is not a virus. It's great and worth downloading, so don't be afraid to give it a shot.
Second, this game's pretty good. I'm a sucker for boss fights, particularly against really big and overwhelming enemies, so if you're the kind of guy that likes to take on massive bosses in games and doesn't like all those little enemies, you'll like this game.
Third, the style and music is great. The little touches that make it look like a damaged tape are great too.
Of course, no game is free from problems. My biggest problem is the fact that you can't scroll through levels. I say you should have two modes, a score attack mode, which is basically what we have now, and a practice mode, where you can skip to any boss you've seen before and tackle it without points or anything like that. But as it stands, it's pretty annoying to have to restart every single time.
The guns have a small problem in my book with how they work, particularly the scatter gun. Sometimes, especially at the beginning when you're still learning, you pick up a gun you really don't need or want at the moment. You should be able to switch between them, maybe with the Q and E keys?
I think you could work on your player communication though. It didn't take me long to figure out what to do with the second boss... but only because I accidentally kept shooting the floor xD Maybe on a game over you can have the scientists reviewing the tapes and they give tips to the player for next time?
If you wanted to keep expanding on this game, LAN based multiplayer and different difficulty levels would be amazing, as well as hunting down and murdering the terrain glitches with the third boss. I found a bunch xD
Oh well. Better go beat that final boss, eh? Good luck with future gaming ventures!