I love this concept, dead simple but surprisingly complex! If you expand on this (more enemy types, node types, etc) you could have a really solid game on your hands.
2 Main issues, sometimes clicking on stuff felt a little unresponsive, mainly after shooting an enemy, like there was some sort of hidden cooldown, that was a little frustrating. Also when you try to shoot more than one enemy at once (since you can hit your own nodes with your shots) it only kills one enemy and the death sounds plays on a loop REALLY loud x)
Got to level 16 before I lost my last node, most of them were friendly fire >.>