Pretty good for your first game! You've got a title screen, some instructions, and the graphics are not bad! As other's have commented, I would definitely take time to add sound in the future. Maybe sacrifice one of the levels if need be. Sound adds SO much to a game.
On a gameplay note, I couldn't get past the first level or wave. I never managed to kick the rocks in the middle for some reason. I even had inifinite life on one play through somehow as my health went negative and was able to keep playing for as long as I wanted. So, contrary to what you said in the game pages description about making it harder, I would advise to go the other way.