Wow, Ed, this is a really fun game! Thank you for creating it and letting us play it.
My high score so far is 2285. It's always those light cruisers firing diagonally that kill me in the end. There's too many shots flying around and I can't dodge them all. Once I lose one ship, my other lives don't Last long because it's pretty hard by that time.
Noticed that F4 switches between full screen and a window view. F1 brings up an empty info screen (handy for pausing the game). You can move diagonally by pressing an up/down key in combination with a left/right key (e.g. up and left to move diagonally up and to the left). Moving down is slower than moving up, which makes sense.