I don't like unlock systems for arcadey games like this. If you could give players like me the option to unlock the guns and levels from the start it'd be pretty nice.
Besides that, I quite like the game. Biggest problem for me really is the crossbow guys bolts fire way too fast for me to even react and shoot out my shield in time.
I think you nailed the simple addictiveness of old new grounds games tho. I quite like how reloading itself places you in such a vulnerable position. I think maybe it could use a timed power-up to spice it a little? Maybe something that increases speed or fire rate? I don't feel the increased ammo pickups is exciting enough-- though for what its worth, I'm still going out of my way to grab them-- gaming habits be damned.
I'm not a game designer so I don't know if that'd ♥♥♥♥ up the good base you got here. But the fact that I went out my way to play more of your demo after I tried it out for a few mins shows you got something good here.
Reposted my comment here incase you're not looking on steam.