These puzzles are printed on nice paper that holds up to erasing. The grids are big enough for candidate lists. I really like the spiral binding.
Level 2 starts with basic and intermediate solving strategies (crosshatching, claims, multiples, remote pair chains, etc). On page 79, puzzle 146 the puzzles begin to get more difficult and require some advanced solving techniques. There are plenty of puzzles at each level to practice using these techniques.
Better than most sudoku books out there which are way too easy, especially if you want to actually use intermediate solving techniques. I'm looking forward to doing the final two books so that I can fully use the solving strategies I've learned.