It's only one of the best picross games if you haven't played any of the great ones.
But it's decent. What hurts it is lack of QoL features, touch only controls, and the bloody puzzle timers.
Some would say it has only small, 15x15 puzzles, but I tend to prefer them - better to spend 5 minutes on a puzzle than 2 hours..
Oh, and yea, skip the second batch of puzzles. There are only 26 new ones IIRC, which you randomly get, rest is just old puzzles that you have to solve without the ability to mark spaces. -_-