This is a fun idea, but I think the "out of control" element holds this game back. I think you could make the levels much more interesting if the blocks dissapeared in a set sequence. The randomness does add a nic arcade feel though, so I'm sure many would disagree with me on this point.
I just can't help but picture levels, where blocks disapear in a predetermined order. I think you could do a lot with that idea.
More elements like the spiked blocks could also enhance this game :)
All in all, it was fun