I am a longtime Sudoku fan, despite my deeply held belief that I am not pronouncing it correctly. I have to admit that, although the puzzles are fun and challenging, they do tend to get somewhat repetitive for me. Maybe I haven't studied enough of the advanced techniques or perhaps I'm simply unable to appreciate the subtleties that present themselves in the various puzzles.
At any rate, stumbling across this Tri-doku book in a local B&N was a pleasant surprise. I thumbed through the book and was curious enough about how the puzzles worked to buy a copy. Once I brought the book home I sat at the kitchen table trying to familiarize myself with all the rules, of which there are a fair amount. Once I was immersed enough in the instructions I dove into my first puzzle with a #2 pencil (more on that later). After many mistakes and frustrations I finally got the hang of it and I am now officially hooked.
The puzzles offer (to me anyways) so many more twists and "a-ha moments" than traditional Sudoku and are much more addictive. Of course your mileage may vary. Given that there are about 10,000x more Sudoku titles than Tri-doku (I think this book is the sole one, in fact) maybe it appeals to a much smaller type of puzzle solver.
At any rate, if you are looking for a unique twist on this phenomenon you should go over to the author's site (http://www.tridoku.com) to read the rules and give some of the puzzles a test spin. If you are at all like me you'll probably be purchasing the book soon after.
Now. The pencil thing. I found that, unlike most other puzzles you might work on, a pencil -- for this book anyway -- is a poor choice. This is more of a statement about the type of paper the puzzles are printed on than the puzzles themselves. I found that a black ball-point pen worked best and -- if you're careful -- was adequate even with the occasional goof. Using a pencil results in dull, very light numbers that don't erase off the page very well. I suppose I could take a star off my rating for this but the puzzles are just too damn cool.