Mediocre
The effects were incredibly anticlimactic. When you're making a shooter, you need to make the player to enjoy killing the enemies. In GeoWars, the explosions were obviously poorly-done, but maybe your experience with flash games didn't allow you to make the effects that you did want, which is understandable. What I don't get is your sound effects. If you want a player to have fun shooting things, you need to make that action not just visually but audibly stimulating.
Also, all of your power-ups were also in the game Neon: the gun power-ups, time-stop, the bullets-in-all-directions, and weapon-speed. I really thought the time-stop effect was cheesy. Cool-Natio's idea was much better, just do black-and-white, not negatives though, that just felt cheap.