Gene Wolfe is difficult to praise highly enough without sounding unconvincing. One can urge people to read his work, claim that he's one of the greatest living writers in the English language regardless of genre (indeed, perhaps the greatest), one can ramble on about his virtues for hours to friends and strangers, and in the end, to those who have not read him, the claims start to sound unhinged, even deranged. "Aren't you overselling him just a tad?" they inevitably ask.
To this I can only say: read some of his work and see. "The Fifth Head of Cerberus" is perhaps the best place to start, not because it is his easiest work (it is not), but because is both fairly compact and an example of Wolfe at his best. The commitment is smaller than if you launch in to the Latro books, or "The Book of the New Sun", but the joy to be had on reading is no smaller. You will know soon enough if Wolfe is, for you, all that his admirers say he is. I say "for you" because taste in literature is inevitably personal, and perhaps you will find that Wolfe is not what you are seeking. Perhaps, however, you will find that he is, and if so, you have a wonderful treat awaiting you.
I suggest that you not read any review of this book that describes the plot. In fact, I suggest that, if you choose to buy the book, you avoid reading overly much about it, looking at the cover image, or reading the back cover copy. None of them will improve your experience of the text. No summary will do you any good, anyway. I could explain the plot of in a couple of moments, and it would in no way convey the pleasure that reading it will bring to you. In fact, knowing anything about the plot at all will explain nothing about why you want to read it, and might, in fact give one precisely the wrong impression about why one would want to read it.
Wolfe is said to have claimed "my definition of good literature is that which can be read by an educated reader, and reread with increased pleasure." "The Fifth Head of Cerberus" is, by that standard, some of the very best literature there is. Immediately after I first read the book, I was driven to read it again. I have since re-read it perhaps five or six times over the course of many years, and each time I find both that understand the book better, and that, like a bottle of incredible wine, aging has only improved the content.
I would normally be reluctant to give five stars to any work, but not in this case. Can this book really compete with, say, "Moby Dick", or "Hamlet", or "Lolita", or "Ulysses" in the canon of great literature? I claim yes, it does. See for yourself.
I will close with a few remarks to serve someone newly encountering Wolfe's work. He is a master craftsman, and makes few if any mistakes in shaping the intricate puzzle boxes he hands to his readers. Every sentence in a book has been placed there for a reason. No detail of character, setting or action is described thoughtlessly, and no detail will be described to you twice. Wolfe does not telegraph his motives or paint a summary on a billboard -- he expects a thoughtful reader. That said, I discourage you from treating his works as mystery stories or as a game to be solved. They are not. You should not be attempting to commit each line to memory, and should not try to drain every last bit of meaning from them on first reading. You will not succeed, and it will serve no purpose. Instead, dive in, enjoy the elegant prose, hang on to the galloping story as it carries you forward, and marvel at the form of the whole as you reach the end. When you inevitably wonder about something you may have missed, worry not -- you can and will enjoy the work even more on re-reading.