Needs some twist to introduce a challenge
The graphics were brilliant (I love the cute squashed earth) and the music was good. I felt the game's mechanics really needed more tweaking though.
In easy mode, I lost a life within a second, another at 2500ish points, then exited to the menu at arounbd 3k. In hard, I got to 8k without having lost a life, then got bored, let myself die and closed the window.
The speed of the asteroids doesn't seem to noticably increase. As we get further, their frequency should start increasing.
I'd also suggest upping the speed - at the minute, it just seems too easy to survive indefinitely and that's a real turn-off.
Lovely presentation though and it's simple to pick up and everything's clearly signalled from the lives to the power-ups.