Okay, potential to be very good.
This game has potential but lacks some critical components to make it worth more than a glance.
Firstly, the aiming is sorely in need of some tuning. The shots do not go where the mouse points, making it difficult to accurately send your missiles where you wish them to go. You should have to fight your enemy, not your control scheme. Along with some needed tuning, it would be very helpful to have some manner of reticule instead of the mouse pointer in the game screen.
Second, there is little evidence that there is a victory scenario. This in itself is not the worst thing, but when your upgrades are all received with so little effort, it makes the very long, and ultimately pointless, grind at the end where the enemy seems to have more and more potential for growth while your tower is forever trapped in it's current form, pointless. Why should I play any further than the 5 minutes it takes to get all the upgrades? No victory, no more growth, just endless shooting until I ultimately fail. There is no motivation to do any more.
If you address only those two issues, you will potentially have a really fun game that people may come back to. Some ideas would be to make the upgrade cycle longer by including many more options to the list, giving the player more choice in how to custom build their tower. If you are going to insist on not having a voctory scenario, then make certain you do not simply increase the amount of points it takes to get what is already available. But an end game is preferable. If you do include an end game, be certain to include some map or count down, letting the player know that there is, in fact, an ultimate victory to be had. Maybe your game does have a victory scenario, but how would I know unless you gave me some way to judge how far along I had come. Best of luck and I look forward to more of your offerings!