Much to my surprise I enjoyed the puzzles. It's a surprise because I used to not be very good at solving them. Or maybe I wasn't interested enough to focus on them to solve them?
I liked all the puzzles. The one exception was the one which I managed to get turned in about 1/2 hour before the deadline! (I like puzzles which aren't ambiguous in interpretation and if I read it one way, it meant 'this' and if I read it another way it meant 'that'. That one was Puzzle 3 - Herbology.)
A favorite was the one with the House Elves (#11). It just sort of solved itself as I was writing it out.