I see you've put much time and effort into it.
The interface and menus turned out very well, I like it.
The training missions could be better. I'm telling you, the majority of players won't bother to read the instructions at the main menu screen.
Use the training missions to teach the keyboard shortcuts. Or at least make it possible to view the key list in-game.
Personally I find the enemy ships very hard to hit, there seems to be no way to adjust your speed to the speed of the enemy vessel ?
Then I read your post where you mention that it is easier with the laser. Such tips definitely belong in the training missions. The player does not know how to play your game, and expect him to be too lazy to read through instructions. Use the training missions to teach the controls and other tips.
I think the sun should look more impressive, try using a sphere with a scrolling lava/fire texture (just brighten it up a lot) and then consider using bloom. Or maybe ask Morcilla (
MPL3D Solar System), the sun looks very nice in his solar system simulator.
The ships could be pimped up as well. There is a normal map shader with a illumination texture stage, this would work great for glowing parts like windows. The energy weapons could use some improvement as well. The first weapon reminded me of shooting tennis balls.
Your representation of space is realistic, personally I would have taken some artistic freedom and added some blueish nebula like areas just too keep it interesting. But that's just me.
Those are some points which in my personal opinion could be improved. Other than that I think you did a great job, and I think it's nice that you are so dedicated to your project. I'm sure it will turn out great.