Hitori puzzle: big and difficult

It’s been a while since I last posted this kind of puzzle. You can read about these “reverse sudoku” puzzles here:
– The rules of Hitori
– How to solve Hitori

This one I’m posting now is going to be a difficult one. I hope. Some have claimed that my Hitori puzzles are not difficult. What do you think?

Hitori 15×15 for January 31, 2012.