Went through all 40 levels, definately a lot less frustrating than the original version of SBTB. The difficulty seemed to fluxuate, but overall it wasn't too bad. Level 33 had my head scratching for a few minutes though :P
I like the little animated touches that you put in such as birds fly, sun shining etc. ...Having unique backgrounds for each level also help add that sense of polish to the game.
Looking forward to seeing what new game mechanics you'll be adding in the future :)