I really loved the effect when time slows down and how the music changed. I also really enjoyed the sfx and music in general. A few levels were particularly tricky for me (particularly 8 and 9) but I finally cleared them, which was pretty satisfying.
I ended up using the 'click right next to the ball to barely move' strategy for most of the tricky spots.
Including an option to skip levels was a nice touch, as we as allowing the ability to unlock hard. I didn't need the level skip but I did try out Hard mode level 1, but didn't get past the first level. I think the levels in general were pretty well designed and the difficulty increased at a reasonable pace.
Overall it was a pretty solid game experience and I enjoyed completing Normal mode.