Solved 1-11, got to 12 and had zero idea what to do.
Came back several days later and it suddenly clicked, solved all of them in one sitting, ending at 3am because I couldn't put it down.
The only thing that confused me a little was the very last puzzle, with the N15 that I assumed was supposed to be the word completely covered by the line. Were we supposed to actually know what that word/phrase is?