I prefered the block graphics! not that the pixel art ain't great, but the other had a strange charm to it that really suited the minimalistic gamepaly.
Also, the "press any key" makes me instinctively switch to keyboard for the sheeps, even if I well know it's mouse-based. :T Speaking of which, it could have been nice to have more variety in the sheer height on the screen, so that you can't merely keep the mouse at the sae place all the time (or maybe I haven't got far enough in the game)
good job!