Please Don't Buy It...
The online games seem to be getting tighter and tougher by the week!
Seriously though, if you want to step up from Winning Low Limit Hold'em, this is the book to get. I'm about half way through it, and it presents some very complicated theory, in easy to read language.
Note of caution, if you are brand new to hold'em, you'll want to get some sort of primer first. This book assumes you know the basics, and have played some hands.