The other rule sets I glanced over. They all looked comprehensive and I'm excited to dig into them on a leisurely basis. To not duplicate lots of scoring patterns, all the common scoring patterns are in the back of the book. So Scott only needs to say something like, "Pure Outside Hand" and gives you a section number to reference what that hands consists of. This allows the bulk of the book (218 pages) to really pack in the rule sets and variants.
There are a few pages dedicated to other things you can do with Mahjong tiles - including a brief section on Divination. Those additions were a nice touch - though probably outside the scope for most readers.
Considering the street price (I got mine for under US$15 shipped), I can highly recommend the book. While it wouldn't be a perfect introduction book to the game, it's highly valuable for the wealth of variations and rule-sets for those who have some experience with the basics. There aren't all that many good Mahjong books in English but this is definitely one of them!
