Hi and thanks a lot for the comments!
To address your points :
-Texture loss when enemies are hit : Indeed, the textures of the enemy become white to make the enemy flash. This is something classic arcade shmups do to indicate damage on their enemies, and a red highlight wouldn't be as effective IMO. White was also used because no enemies are entirely white, whereas some are red and could blend in with the red highlight.
-Adding effects to the explosions : Yes, flashy and cool explosions are important, you are right! I'll try to spice them up a bit if I can.
-Fire effect : Because the background scrolls in 3D, having the fire as a flat object may make it stand out like a sore thumb, but I could give it a try and see what happens. In any case, the effect itself isn't that great, so there's room for improvement.
-Pause menu : Input is rebindable through the little window that appears before you start the game proper, so you should be able to replace Space by Esc if you wish. Space was used as a default because it is much easier to reach while playing, but you should be able to set it up to have Esc do the same. As for making the pause menu button also close that menu, that's a fair point. I'll add it in for the next release.
-Flying tanks : The tank-like ennemies have boosters on the back of their sides, but there is no jet exhaust effect as for now. Maybe that's also why them being able to fly looked odd to you? I should add effects to convey the idea that they can be propelled through the air.
-Blue Lasers not always hitting you : Were the lasers moving through the mecha's white sphere? If not, it makes sense that you do not get damaged but otherwise, it is a bug. I will investigate into the matter.
-Gray Sky : The first stage takes place during the morning and the sky actually becomes clear blue during the second level. You are right that it is still too dark compared to the rest of the colors. I'll look into it.
-Emily dialogue during the game instead of only in the tutorial : I didn't want to impact the pacing with dialogues that people will skip or disable after the first playthrough; however I have been thinking into ways to integrate some snippets of dialogue during the stage intro sequences and/or after defeating a boss. As long as they take place at the same time as the other stage transitions, they shouldn't hurt the pace so why not.
-Difficulty levels : As of now, I haven't planned any difficulty modes, because balancing them all would increase the game's scope way too much. Instead of balancing a single game, I would have to balance three variations, which is much trickier. Maybe later, but that's not in the works right now. I still take note about the boss patterns' difficulty.
-Background camera movements : The background is definitely independent from the player. I wanted to have some more movement compared to the classic left-right for a more cinematic approach. Because the player doesn't interact with the background, I can have some more dynamic camera movements. Though it's still possible that the effect doesn't look quite right yet.
-More shot types : The first boss fires some missiles, but it could be cool indeed to have some other bullet types in the stages themselves. I'll think about it.
-Friendly units : That idea would go against the game's design as you are pushed to kill everything as fast as you can. Units you shouldn't kill would be very distracting IMO.
Thanks again for the feedback, it was pretty useful.