It needs a LOT of work
All the clicking gets boring after a while. The powerups take ages to buy, and the turrets don't seem to work effectively (at least I didn't notice the difference with turrets or without). I would rather kill a LOT of guys with one shot than click multiple times to kill one. Aren't you supposed to be a sniper after all? Plus, that guy in the corner is annoying and TOO distracting. You should make it smaller and reduce the time before it dissapears. Also, you should move that bar at the far left, since it blocks some of the units and you don't know if they're shooting or not.
Overall a good concept, but not very well executed.