For what it is... it's awesome! i'd give it 4.5/5... just one small problem, when you start, it doesn't give you time to get you fingers on the appropriate keys. maybe a "press space to start" button?
Also, i think if you elaborated on the game, put more in, made more modes... or whatever. it would be awesome.
i have to agree, its too easy, i unlocked everything after beating it on my first try :P. but it is quite fun. it could have some improvements tough, like an upgrade system of some sort. 3.5/5