Could be better....
graphics - ok, but could be quite a bit better. for example, how about instead of a boring stripe changing color for the tower, something is added, i.e. a laser or machine gun. also, ive heard that compressing the game can make it run faster. you should also add a higher frame rate.
style - neat, gives a new feel to the defend your base concept.
sound - its relative to the game but after a few levels can get repetitive and annoying
violence - none that can be seen. you should add "bullets" or something else that gives the signal that the unit is hit.
interactivity - the buttons are nice, but can be touched up a bit. for example, the star not having a pentagon in the center.
humor - you could add a funny animation that shows the unit dying, like the tank blowing up, for example.
other things:
spacing - fix it so the buildings arent half off the "map". also, some of the units look like they're connected, and not just one unit after the other.
animation - making look like one unit is moving at a relative speed, like the soldier not moving faster than the tank, or making so the soldier looks like its walking, not sliding over the ground as though its ice.
besides all of those other things, its not bad.