I find the puzzles challenging enough, but the app is constantly closing itself out and then when I try to go back in its just a black screen. It will often open to a puzzle Ive already finished and show it as half done. There are a couple other glitchy things as well. So basically, its all right if you have the patience to get through the glitches.
Bea_minor3rd about Crossword Light, v2.74