The problem with a slow charging shield system like this is that the best strategy is to stand still and not play the game for a while until they come back. Have set charging stations or have them charge faster if there are no enemies around. You don't ever want the player doing nothing on purpose.
Why do flash games always send your ship at warp speed to the top left corner if you go a smidge off the edge? Just keep the ship at the position you last saw the mouse. Don't poll, get 0,0, and assume that I am for some reason able to teleport my mouse to the stupidest place on the board to be. Every game does this. Two line fix.
The game does keep the ship at the position it last saw the mouse. And it only updates when you move the mouse. If moving the mouse offscreen sends you to the top left corner, the problem is something else. And it doesn't happen when I try it. It's something on your end.
It might make sense to release a "game" where you flip random cards and take a nap before something like Kingdoms:CCG comes out. But to follow right on its heels is kinda sucidey. There is an actual game to play over there.
Best first 3 seconds of gaming ever. "Ok. So I GAH!" Only thing that would make it better would be to explain why the guy has his particular condition. Like a timer until death lasers. Otherwise have him do it one last time in the credits.
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The game does keep the ship at the position it last saw the mouse. And it only updates when you move the mouse. If moving the mouse offscreen sends you to the top left corner, the problem is something else. And it doesn't happen when I try it. It's something on your end.