Honestly I don't really see much of a review here, so step aside, and allow me DR XYZ to attempt this task. First of all some little truth has been spoken about this volume, viz that it was published in 1821 and a second edition was published in 1856. What mercet fails to mention is that the 1856 edition is a much longer version, padded out in what is generally thought to be an inferior style. Thus the 1821 edition is the one that is normally read today. I've never seen a copy of the 1856 edition, but one copy I owned did contain selected passages from the 1856 edition, which were interesting only in part (more dreams, details etc), and these were clearly selected for interest.
When I first read the book I was surprised by how much of what he wrote wasn't about opium, and opium eating. He does write in a scholarly manner (bear in mind that he spoke fluent Greek at a young age, and was a good classical scholar) and uses such terms as pharmakon nepenthes (in Greek), pandiculation, evanescence, and many others that require either a footnote or a google to decrypt. I like this as it is a book that will extend your vocabulary. However despite the erudition, the style is still somewhat clunky. It sparkles in places, but often drags. There's a charming vignette of a cottage scene of opium eating in winter, and some good stories. I like the one about the Malay who comes to call for example.
What he says about opium (and he essentially dismisses any medical opinion except that opium is brown, expensive, and a lot of it kills you) is often contradicted by his own experience. He seems to think one doesn't increase the dose and yet he did. He'll justify this by talking about his real and genuine medical complaints. He claims opium is a stimulant, and criticizes those "Turks who take opium and sit around on logs as stupid as themselves" (this is misquoted from memory), and yet claims his greatest pleasure is sitting alone watching the sea. I'd take a lot of what he says with a pinch of salt, as like so many addicts he has a warped view about his own using of drugs. For example when he says that he'd quit or cut down to a very low dose (I don't have a copy to hand, I'll edit this later if I remember) and stayed their for a period of quite a few months, and got no relief of withdrawal symptoms, I find this very unlikely. This book is of no use as a how-to guide for opium eating, but is a window into a different world. On occasions De Quincey shows genuine perspicacity and wit, but other times he slips into self-indulgent prose. The dream sequences I didn't find that interesting. I usually sag mentally when I know I'm about to be told someone's dreams. I think he must have had an usual mind to begin with, and the dreams he describes (often nightmares that seem unending) are peculiar to him, and are not representative of what a normal person will experience under the influence of opium.
I was drawn to it as a "druggy" book, but have reread it several times because I found it charming and worth wading through.