Doyle Brunson first published the classic Super System in 1978. Today it's mostly famed for Brunson's monstrous, folksy, money-winning no-limit hold'em treatise, but what Brunson created with Super System was far superior to a single book on a single game. What he created was a manual of advice on all major types of poker being played in that day and age from the foremost minds in the game. That Sklansky, author of the Super System chapter on high-low split poker, would nine years later publish his own textbook for students of all poker games is no surprise given Brunson's admiration for his thinking on the game.
The Theory of Poker is inarguably a classic text on the American game, if for no other reason than its explanation of the Fundamental Theorem of Poker, which begins like this: "Every time you play a hand differently from the way you would have played it if you could see all your opponents' cards, they gain; and every time you play your hand the same way you would've played it if you could see all their cards, they lose." That basic explanation has become gospel, the basis for most of the published advice on the game since it was published. And why not? It's the kind of explanation that allowed a vocabulary of describing poker to be developed, and that vocabulary gives any student the power to make the best possible decisions in any situation.
Among some people The Theory of Poker has a reputation for being dense and difficult material. The problem isn't so much the difficulty of the material, as it is that Sklansky is a mathematician first and a writer second. (Come on, do you remember any engrossing reads in high school Algebra?) Your head may not spin from the beauty of his prose, but the information Sklansky presents might just be worth overlooking even if you do require Pulitzer-quality writing. The feeling of reading a textbook is hard to get away from, but anyone who's serious about understanding the basic building blocks of poker should have no problem with that. The book is arranged into 25 chapters, most of which are under 15 pages in length. These short chapters take basic poker concepts and define or explain them. Then, examples of the concept in play are shown and discussed. The only thing really missing is a workbook with exercises to complete after you finish each chapter.
Most of the concepts are so fundamental to understanding poker that they've become keywords for poker discussion boards all over the internet. Even if pot odds, the free card, and the semi-bluff are all concepts that most players serious about the game understand on some level whether or not they've read The Theory of Poker, there's definitely something to learning these concepts from the original source. Sklansky's analytical thinking teaches you not what to do in specific situations, but what factors to consider before deciding what to do. That's a different approach than most other books, which tend to focus on a particular game and sometimes give very particular advice for different situation without a basic factual explanation why.
While The Theory of Poker may not be the only book you want in your poker library, it is definitely one you should have. It's the kind of book that's good to pick up every couple of months or so just to brush up, and then once a year or so for a thorough review. Like any classic, you can get something from it every time you pick it up. Other poker books provide more information on nuances of specific forms of poker, but The Theory of Poker provides a way of thinking that can allow you to successfully play any game of poker. A thorough knowledge of the thought processes espoused in this book is the sort of tool that can help you to get more from the other poker books you own. If that alone isn't worth the price on the front cover of the book, there's probably nothing that is.