Thank you very much for the kind feedback :)
If I update the game I'll maybe try enabling vertical movement. That would make homing missiles a LOT less threatening for sure. Some balancing might be needed.
One idea would be not to allow free vertical movement, but to give the player a "boost" button to push you up the screen for only a split second, with a cooldown.
Powerups would also be great, but would also need balanced. Like really powerful power-ups that only last for a short time, or power-ups that are only marginally more powerful and don't cause the game to be lost effectively the first time you die and lose your weapon. I think some classic shooters will always spawn power-ups when you re-spawn, that might be good...