I have wasted far too much of my life on Sudoku puzzles. As a permanent substitute teacher whose days often consisted of babysitting, interspersed with the blessed relief of real teaching, I could not read all day or even during a study hall for an hour. Printing the "monster" version from www.dailysudoku.com
allowed me a portable amusement.
I like the 16 block puzzles, I think, in part because they test my abysmal eyesight. The 9 block puzzles are more difficult, most likely because they are asymmetrical.
Mechanical pencils help because they produce a finer line and don't need constant sharpening. Those tube-erasers in plastic cases help as well.
Other sudoku addicts have said that some 'hard' puzzles are quite easy while some easy ones are aggravating. I no longer attempt the solve the easy, draw and play, four block puzzles on line.
Because of sudoku, I have spent a fortune on ink cartridges, printing the daily monsters!