Ok I see that Luftrausers had a similar impact on you as it did on me. I loved that game and frankly I think I am going to reinstall it now after playing this. Obviously comparing the two is a little unfair, I think they had a little longer than 7 days to craft that game. In fact, gimme a second, I'm gonna play a round of Luftrausers right now and then get right back to you. Please hold.
Okay. Yeah. Still rad. My skills have atrophied though, yikes. The two games are more different than memory might suggest, different controls and upgrade systems entirely. However, if I were to suggest you borrow one thing wholesale from Vlambeer's design, if you allowed the ship to auto-repair itself when the player wasn't firing the weapon, that would take a lot of edge off the difficulty and offer a push-and-pull in gameplay, attack vs. evade.
This was super fun and I'm stoked about it. Let me know if you're developing it further, I'll gladly show up for playtests at the very least.