Just finished it. I liked it. It took a while to finish because it wasn't as quick a read as the latest Tom Clancy book, but overall well-written and enjoyable. Here are my opinions, because it is my blog after all :).
Let's start by laying out there that this book is not for beginners. Before reading HOH a player should at the very least have played in a couple of No Limit Hold Em tournaments and spent some serious time working on their understanding of the game. I think this should probably be the third book someone should read on NLHE, after any of a dozen good introductory books and Super System (I haven't read Vol. II yet). I started with Phil Gordon's The Read Deal, which had some entertaining stories and a few viable tips on the concepts of play, then read Super System and a couple of others. But I recommend at least getting an intro book and SS under your belt before tackling HOH.
And this book will not be for everyone, because not everyone wants to play tournaments. If that's not your thing, don't bother. Not that I don't find the concepts in HOH Vol. I very useful and salient to ring game play, but it is geared primarily toward tournament play, and decisions that are wise when your opponent can't reach into her pocket for more ammo are downright stupid in a ring game.
That all said, I found it pretty useful. I tend to be an aggressive player (chorus of DUH!!! in the background), so the tips on more conservative style of play I found helpful for tempering my aggression with mathematics so that I can make the more frequently correct play. Harrington stresses pot odds over and over and over again, so by the time I got about 2/3 of the way through the book, I started to get it. His explanations (and re-explanations) of pot odds were very useful to me, especially in helping me understand the appropriate bets to make and to call (which is, after all, what pot odds are for, dumbass!). The explanations and examples of pot odds were very good, and I have found it helping my ring game play as much if not more than my tournament play. But I'm still new at this, so that's to be expected.
Dan describes himself as a conservative player, and I'm sure that compared to folks like Gus Hansen he is, but he still advocates an aggressive style. The points in the book that I liked were the times when he stressed that your entire poker career is one long game, and as long as you are making the +EV moves, they will in the long run pay off. This is hard to remember in the heat of the moment, but will help fend off tilt in the future (maybe). Another interesting statement that Harrington makes (steals actually from Sklansky, with attribution) is that your job as a poker player is not necessarily to win the hand, but to make the right decisions every time while putting your opponent into a position where she makes a mistake. I like that.
The book is divided up into sections like Starting Hands, Reading the Board, Betting Before the Flop, Betting after the Flop, Betting on 4th & 5th Streets, etc. and each section has a set of problems after the chapter to illustrate points from the section. I found this pretty interesting, since these problems are taken from actual hands, and frequently Dan goes into a long explanation of why you should behave in a certain way in these situations, and the player who really played the hand did something completely different! Not all of these real-life situations work out to the detriment of the folks playing, proving that at times poker is as much about making the wrong move at the right time as it is making the right move, period (I think that's an Iggy-ism).
So I liked it, that wasn't quite as clear a review as I'd hoped for, but I just got out of rehearsal and sat into the $1 Limit O8 tourney on Stars and those folks are loopier than me.
PS - nicknames still needed, but I like BigPirate's suggestion of Falstaff - Shakespearean, and a Beer, too!