Okay, so having given it a look, and thought about it a bit, here's my feedback for you:
I really think you've nailed the flight/combat system, and the feel of watching you fly around is exactly right. That's not easy to do, and major kudos for pulling it off on a mobile platform. I also really like the simplicity of your controls, everything seems to be there, and seems to work as intended.
On the improvements side, I think you'd be best served with focusing on two things - consistency and punchiness. By consistency, I mean that the icons for your controls all feel slightly different - the control stick looks like a different artist made it from the weapons/speed controls on the right. And the right hand side has a mix of icons and actual pictures of the weapons. I'd really reccommend making all of that look exactly the same - figure out a good looking skin for your controls and make everything match it. It will be less confusing for the player, as well as make the game look more professional.
For Punchiness, what I mean is that you need to make the actions you take in the game feel impactful, engaging, and fun. You should feel badass when you fire your weapons - right now that action feels almost subdued - the weapon effects aren't impressive, and there's not really any visual feedback that you're firing besides little streaks of light shooting from the sides of the screen. Same with the explosions of enemies - the fireballs are pretty standard looking, with very little animation or force to them. Like orange balls that fade in and then out. They need to be much more engaging. Try for something that makes you feel like you've earned a lightshow - something that makes you *want* to blow stuff up, just for the joy of watching it.
Here's a good reference:
Sure the movie is terrible, but when that space station goes up, you can feel it through your eyeballs - the explosions feel vicious and solid - like really dangerous.
That leads into the second part - on a mobile game, you can't rely on sound design to carry player feedback. Speaking from experience, most mobile players will play your game with the sound off. That's no excuse to skimp on the music or sound design, of course, but if you want the player to be sure to get the feedback you want, it has to be visual. That means subtitles for audio, and visual cues for every interaction that happens.
Here's a great rundown on exactly what I mean.
Anyhow, I think you've got a great foundation, and the game looks fun.
Good luck!