I especially like the way Heisig takes great pains to teach you how to learn new characters on your own, once you have moved beyond the 2,000-odd characters which are treated in this book. In perfectly graduated steps, he weans you off of stroke-order diagrams and his memnonic stories; Before you know it, learning a new Kanji on your own in a matter of seconds will become second-nature to you.
Best of all, if you follow his instructions religiously --especially at first, when you are tempted to stray back to your old "I'll write it a thousand times until I 'recognize' it" method-- you will be amazed at your long-term retention rate. Once, I put the book away for a few months and was able to start right back where I left off, without having to review, or relearn characters!
This book is well-written, concise, and fun to use. No more excuses, buy it and start reading Japanese today!
Much has already been said about this extraordinary volume, but there is one very important point which has not been raised, even by Heisig himself. Beginners in Japanese - please take careful note.
Put simply, mastery of "Remembering the Kanji I" (along with the simple hiragana and katakana scripts) is analogous to mastery of the 26 letters of our own English alphabet. These 2000 or so characters - compulsory learning for every child in Japan - are the building blocks for almost any Japanese word you would care to imagine.
Why is this so important? Well, it suggests by far the most efficient way for a beginner to learn Japanese. If the beginner can complete this volume before learning a single word or attending a single class (completion, quite remarkably, takes no more than 3 months full-time), then he or she is at a huge advantage over any other student of Japanese. Why? Because every single time that student learns a new word, he or she can learn it in conjunction with its kanji form if it has one.
This is a vital point. Most people when asked how they became proficient in Japanese will say that hobbled along for several years using mainly hiragana and katakana, and, worst of all, the romanized form - romaji (personally, I spent a whole year learning Japanese using romaji). However, to do that is really shooting yourself in the foot. It is a gross inefficiency for three reasons. Firstly, you will have to learn words twice, or even three times (if you used romaji, then 'upgraded' to hiragana and then kanji). Secondly, your memory won't be able to benefit from being able recognize ALL of the kanji you see around you on a daily basis in Japan. Thirdly (and perhaps most importantly) you will never have any insight into WHY a word sounds like it does. For example, learning the word for post office clerk - "yuubinkyokuin" - in romaji is very difficult because you have no idea whatsoever of the kanji building blocks. However, those sounds are there for a reason, and break down into four kanji which, using Heisig's method, you would have learned as 'mail', 'convenience', 'bureau' and 'employee'. Needless to say, these four sound-units appear in hundreds of other words, and this gives an internal logical to vocabulary learning which simply does not exist otherwise.
I am slowly recovering from post-romaji stress syndrome. Believe me, it is the worst habit you could ever get into. Once I realised the importance of the above, I resolved not to learn a single new piece of Japanese vocabulary until I could write it in kanji too. You should do the same. If you know your 'ABC', you can be confident about learning any Japanese vocabulary you want to with considerable ease.
p.s. I would recommend two more aids in addition. Firstly, as other reviewers have noted, Heisig's 2042 "Kanji study cards" are very handy for learning the 'yomikata' (the pronunciation). And secondly, something that hasn't been mentioned is "Kanjican" by Kanjisoft systems (available on the web). While by no means a perfect program, it is designed to accompany Heisig's series, and allows you to enter both Heisig's and your own stories (to replace the author's quite frankly abominable ones), and then be tested randomly on each kanji. Very useful indeed, since you need a place to record your own stories.
Particularly if you are living in Japan, and don't have full time to study, Heisig's system is frustrating. After Book One, (which at 1 hour a day takes about 1/2 year to get through) you know how to write "gall bladder" but can't read the sign in the local depaato that says "iriguchi". Also, many of the keywords are quite far from the kanji's true nuance (i.e., "nothingness" for "naku naru"). Contrary to Heisig's claim, the original keyword, (like the use of romanji), will forever color your understanding of correct Japanese. I.e., the criticism that kanji must be learned in context is to be taken seriously.
I do recommend buying Heisig's book because the imaginative memory system is brilliant and will inetivably aid your kanji study.
However, most important:
I don't recommend using any single author's system for learning the kanji, no matter how brilliant, fast, or self-contained it may seem. Instead, develop your own system based on your own personal learning style. As for me, that's a flash card system based on imaginative memory, pictographics, historical derevation (via. Henshall), sound associations and an ordering system based on the not-yet mentioned book by Habein & Mathias (The Complete Guide to Everyday Kanji - EXCELLENT), and my daily encounters with the kanji. However, for you, I hope, the system will be different and your very own.