A solid start. A couple needs:
More than 1 projectile
Faster projectile
Friction-less surface
Possible background change to ground combat and a tank change to the NG guy
Get rid of = and replace with :
More health = more fun... so more health
Silence is the enemy of video games, add some sounds
reset button
a solid start and very nearly a fun game, when it is complete. This plays like a pre-alpha proof of concept.