Really neat game! I really want to try to make something similar to this some day, flying in an open area like this is really cool. I wish the plane was a bit more steerable, but maybe that was something unlocking the upgrade allows for. I got really stuck on a challenge to fly upside down near the ground.
I would wonder what it'd be like if the camera rotated with the ship, I think that might make that kind of challenge a little easier as trying to fly upside down is mostly difficult due to the inverted control feeling.
Otherwise though, really cool design and sound work, and the shader work is really interesting too! I don't think I've seen post processing like this before, it feels pixel-ey but a bit more dynamic, I spent a lot of time just kind of watching the shader trying to see how it's producing the visuals lol