It's Good for a 5 Minute Break
If I needed a quick break from work and didn't want to get wrapped up in anything, I would probably play this a few times then get back to writing my paper. It's entertaining for a bit, but like you said it lacks creativity among other things.
I'm all for shooter games, and retro one's are my favorite like Hogan's Alley for the NES, great fun. This just felt like a 'train wreck' (your words). The retro music was good, but it was reset for every new level, so all you heard were the first 30 seconds over and over again, and it was always the same song. You could have made different backgrounds and had different music for every 3rd level or so, that would of helped. You did include a mute key so at least I had that.
The shake to ammo reload was a little tedious, especially when a lot of stuff starts flying around, a left click or an 'r' press would have made game play a little smoother. The ammo bar itself was just distracting and made it difficult to find the cross hairs. A bar on the side with an ammo count and a larger targeting cross hair would of been a better option.
The bombs were just a pain to deal with. It's not because they gave you minus points, because I never really looked at the score, but more so for the fact that in later rounds they would get hit with exploding pieces of actual targets. If a bomb and a target came near each other then it was pretty much you're taking a hit either way.
Last thing was that after shooting your upgrade the next round started right away. This really isn't an issue in the first few rounds, but as you progress it puts you out of position for the start of the round if you're selecting rate of fire or ammo upgrades. A few seconds before the next round starts would be very helpful.
In all it's not bad for a game made out of a lack of creativity, and like I said it was perfect for killing a few minutes while taking a 5 min break, so thanks for that.