Getting to mission 6 is the best I can do, both without and with upgrades.
I might be biased because I gave the feedback on inertia, but it feels really good now, especially shooting down missiles. It works really well with the machinegun weapon. It also feels great to tip toe out of drifting and shooting between a bullet hell of projectiles (even if it's mostly by luck) - you can pull surprising maneuvers even though it doesn't always seem perfectly controlable. Avoiding the enemy shooting 3 yellow projectiles by flying between them feels great for that reason - you should alter the attack pattern to emphasize on that more often.
Down arrow could get some use for stopping inertia or tight evasive maneuvers.
I think there are a few problems left. One is lack of control at high speeds which should be fine to buff way up. The other would be camera. Some missiles are hard to react to when coming from off screen, though it happens rarely. As the last resort you could have warning symbols at the edges of the screen about incoming projectiles and enemies.
The game gives you lots of freedom but tactics feel limited outside of prioritizing ground forces - you just focus on moment to moment combat while fighting aerial enemies that all behave similarly, just with different projectiles. Having enemy formations, and a very limited and distinct enemy roster per level could be interesting.
Laser sucks because of low damage and precise aiming required, it's good that it's a secondary plane now. Nuke drive is interesting, but definitely for advanced players. Bullet time is nice, but I think player should control the duration.