The game itself is really good. But the constant attempts to get somebody to purchase something ruins the game. 3/5 for content. Would be 5/5 without the "buy" buttons
If you're looking for a free version of Guitar hero, you could try frets on fire. It beats this by a long shot. You can use the net to find songs you want to play, instead of playing garbage you've never heard of
This is not called Gravity Master. It is called Crayon Physics. A basically identical game was created more than a year ago, with several levels that are basically identical. There were less levels, but the concept is not original here.