Pretty good stuff, I look forward to the final version on Steam. I will say though, considering the nature of the mixing of guns, it would be great to have an area to sandbox and test the combinations rather than having to go into a level to test it. I know in this version we only get 2 "upgrades", but I assume in the final version there are a large number of upgrades and a large number of weapons which would make a place to test weapons essential (IMHO).
I didn't notice any difference between post processing on/off except in the menu.. (it blurred the background) in game looked exactly the same. Also noticed that your ammo seems to hit the side of the screen while some enemies (the monkey) can shoot at you from off screen. But sometimes it seems like even though your shots hit the side they go through (or the enemy is just off screen). Either way it would be nice if that was consistent.
Overall, again, great fun little game, can still use some tweaking before I would pay for it, but I think you have something good going on here.