I really, really, really enjoyed your game! It was a lot of fun. Great combat, and I enjoyed developing different strategies to avoid enemy fire... weaving around them, using cover, etc. Here's my feedback...
1. I got the 23mm Cannon first. A tutorial came up telling me to press X - Y to switch weapons, but I only had that. It was confusing at first because I thought I was doing something wrong by not being able to switch weapons. It wasn't until I got the Energy Cannon that I could finally do it. Perhaps the tutorial only pops when you get a second weapon?
2. Level design is laid out great but some additional decor would help. Right now, the walls and blocks are a bit plain. Maybe add in some wires, textures, and even broken edges and dents in the walls. Everything is super straight, clean-cut, and blocky.
3. The ability to adjust individual sound types: music, ambient sounds, and sound effects. I love how the music picks up during battle, but the sound of the fighting drowns out the music (gunfire, explosions, etc). I'd love to hear the music more.
That's it, though. The ship and enemy artwork is really good, I love twin-stick shooters, and the ability to swap weapons (once you get multiple) is nice. I love how the energy cannon destroys shields faster... forcing you to swap weapons frequently. You gave each weapon a purpose. I like that. The rocket was a nice weapon/addition as well! I'm giving this a follow and look forward to the full game!