My only suggestions are a restart, mute, and (maybe) pause buttons. They'd probably be best placed somewhere at the bottom of the screen. Otherwise it's great!
WASD controls would be nice. It would be ok with out it if we didn't have to use the mouse at the end of every wave. Also when I upgrade a gun it seems to increase rate of fire if I repeatedly press space but not if I hold it down. Intentional? If not, please fix.
Go backwards at the beginning and make your way through the entire game back to the beginning again and continue to go back. You can watch the time bonus timer tick down.
So much to say about this, I can't say it all... so beautiful. It doesn't "hold your hand" like a lot of games today. I had a hard time letting go in the end. I definitely want to play this with my surround sound another day when it's not so late at night.
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Thanks .. will do [Edit : added pause, restart and a couple of tweaks :) ]