Awesome fun with some major flaws
Gameplay was excellent. Very smooth, very fast paced, very fun. Lots of guns to choose from, lots of variety in the levels. You were absolutely spot on, there wasn't a single thing you could've done better in that aspect.
However, I have some major gripes about this game. First off, you can't switch to weapons you've already bought. I started off upgrading until I got the battle rifle, then I wanted to go and get the laser cannon. I went and bought the laser, but wasn't able to choose my battle rifle. I was stuck with the laser. This made my weapon points I gained in the end worthless. I had no reason to go out and get any more weapons, and had everything else powered up. So at the end of the game I had like seven weapons points and nothing to do with them. Another thing. It was difficult to keep my health up. I either had to wait until a rare health pack dropped or upgrade my overall health. After I upgraded my health to full strength, I couldn't buy health anymore. That's another glaring flaw. Thirdly, after I beat the Doom Machine, it didn't allow me to play the rest of the levels. You need to make it so you complete each of the levels before facing the boss.
All in all, gameplay was stellar. Dude, you are a fucking genius. This was a lot of fun. If it wasn't for the cons I mentioned above, this game would be fucking epic. Please heed my criticism. I will definitely be playing more games from you. You obviously know what you're doing.