I have been pretty much way into crossword puzzles the past few months. Late this summer I purchased a book of 300 crossword puzzles and scribbled away every day. I just completed them all, and that includes going back to the few I skipped and completing those. I have a few more shorter books of them but I just got introduced to KENKEN.
This was a holiday gift from my wife, who was aware of my puzzle fanaticism and who thought I might enjoy the new challenge. I have. I have been somewhat into Sudoku, a craze that most people are aware of by now. KENKEN is similar to Sudoku (a 9×9 grid with some of the boxes filled with numbers, the goal being to fill in all the boxes without repeating a number in any horizontal row, vertical row or smaller 3×3 grid). The difference here is that some math is involved.
The book I have starts with easy puzzles. The grids are 3×3. I blasted through them but they gave me a sense of how to solve the puzzles. The book ends with 5×5 puzzles. These are still relatively easy and I am afraid I will have to advance to more difficult ones. Here is a fairly easy example (from www.Kenken.com):

Easier KENKEN Puzzle
And here is a more difficult example (from Wikipedia):

A Tougher One
As you can see, the first one has simple addition and subtraction, while the second one also contains multiplication and division. I am ready to leap fully into those.
So far I have done well but I am still working on the easier puzzles. I will need to go out and get a more advanced book. I am hooked. Sudoku is fine. I have had some fun with that. But I never got jazzed on it the way I am with these. I will not give up on crossword puzzles. I still have lots of those in the house to work on. I will, however, be busy with KENKEN for a while.