Not bad but..
The controls are really stiff. If you're going to use the mouse to aim, why limit it to only diagnally and up, down, left and right? Also, once your tree dies it does get really, really, REALLY boring. Especially since theres no way to make your main gun better and enemies don't drop power ups.
That said, it is fun. The tree giving gifts randomly makes the game way easy though once you increase its stat. But after getting to level 35 I kinda got bored killing the same enemies over and over and over.
Needs more variety obviously. Maybe some "Bosses" or something else beyond wave after wave of the same stuff.