AWESOME GAME! I didn't want to write a review before I finished it, and I just did, with 11680 points. Great graphics, good music, lots of creative levels and lots of different tools to use. One of the few puzzle/physics games that I actually had the patience to finish, even though I like many of them.
Level 16 is not impossible at all, I beat it on my 5th try and I almost had it completed on my 3rd try. Always put your cannon at the same place (right next to a bus for example) and when you find an angle that works well (I think it was 104-107 degrees for me) keep shooting at it with different power (about halfway to the max worked well).