Hi Rory,
Yes, there are three stages of rocks, they start large, then you get a medium sizeed one then finally a small sized one, admittedly the smaller ones are more difficult to hit! The movement in the game is the same as the original Asteroids game, in fact I borrowed the code from one of the example scripts that come with Contruct 2, and it can take a while to master, I find small thrust movements are best and the use of turning in the opposite direction and applying thrust to slow down.. Practice makes perfect I guess! Glad you enjoyed the game :)