Progress through the game and as you get better updates, play the old levels again. Then you can reap the stars. Better than playing a level over and over (except for the 10x achievement ;) ). + to keep this alive.
Sorry, but this game is just clumsy. Can't attack while moving, how dull is that? Clumsy interface, unresponsive interface, "reduced" gfx ... you can do better surely.