The first thing that I notice right away is that the start button is difficult to see. There should be a different outline or maybe even a simple gray or black rectangular background that would make it more evident. Also, when you are done with a game there isn't any replay button. You actually have to refresh the page to get another shot of the game... kind of takes the fun out of playing it and would be much better if it had one.
Other than that the artwork and animation is really well done. I really like the style and it all in all looks amazing. The small attention to detail such as the clouds moving in the background are great. I do recommend making the airplane more of a background feature. It looks good, but if it were more infrequent and farther away it would be better.
To add a little bit of a challenge I recommend having the blocks start from different sides of the screen at random. I don't agree that physics should be included in this game because it would be impossible to get much more than 10-20 blocks while I was getting over 100 this way. I think it would kind of take away from the fun of the game if the levels only lasted a minute. I do like that the higher you get the more the tower sways.
The sound effects were a little overbearing. They should be toned down a little and there should be some sort of background music. The mute button was a nice touch though. If the airplane were moved back you could even add in some distance sound effects for that.