Very hard and a ton of fun!  Though I will note, I got to a point where I could just run away and have no enemies on my screen for several seconds.  I had my greatest success just spamming left click off screen and hitting things at random.  

really interesting game... was thrown by the massive wave of combat for the very first interaction.

I must admit, I'm a sucker for any game that reminds me of classic Asteroids. Even though that game came out long before I was born, it's one of the few games I could ever get my dad to play with me on a regular basis growing up. So it has a very special place in my heart. This game is immediately comfortable and familiar to any player of Asteroids, but is different enough to stand on its own.

Love it. It is so hard and brutal. You might need some walls around to indicate end of your flying zone, and some sort of health system, like regen, shields or healthpacks. I think if you introduce difficulty incrementally that will bring more challenge. Other than that - very cool game!