Too difficult, too boring.
The game literally boils down to "click enemy sprite enough times before time runs out." And then the enemy moves so fast that, even with a predictable pattern, you will miss if you are just a frame too early or late. This is most certainly not helped by the enemy jumping out of the screen and becoming momentarily invincible. And even all this would be forgivable if you had some way to block attacks; that way, even when your clicks miss most of the time (and they will), you could at least survive long enough to actually win.