It seems that people like this book a lot or don't like it at all. I must admit, I don't like it very much. However, I think it depends a lot on: 1) your biochem background, and 2) your personal reading style. Someone mentioned to me that Harper's is like a graduate school text - full of detailed information and appropriate if your background in biochem is sound. However, most first year med students are not biochem majors and need a text that is easier to read (and enjoy). I bought Harper's 26th edition and also Lippincott's Illustrated Review (3rd ed.). They both cover similar topics (not necessarily in the same order), but they differ (significantly) in the way each presents the material. Different chapters in Harper's are written by various authors which creates a glaring inconsistency throughout the book. Many of the chapters are well written but some are just plain awful. The chapters that are poorly written make it difficult to nail down the main points. I often find important information embedded in the book's "essay-type" format. Illustrations are ok, but nothing to write home about. Biosynthetic pathways, for example, are squeezed onto one page with very small print. Sometimes these diagrams are so "busy" that it takes more effort than should be necessary to untangle the important concepts, and quite frankly, is simply uninteresting to look at.
Conversely, Lippincott has wonderfully full-coloured illustrations that are professionally drawn, easier to understand, get to the point, and are visually interesting. Besides the great illustrations, the text throughout Lippincott is consistent, clear, and concise. Topics in each chapter are broken down in easy to digest sub-topics and the entire text book is superior in its organization compared to Harper's (which is basically a compilation of essays). Important concepts stand out and crucial information is not couched as it is in Harper's. However, like I said, if your background in biochem is strong, then you already know what is important and Harper's may well suit your needs. My suggestion is: if you have a strong background in biochem, don't mind superfluous language (i.e. "essay-type" text), and don't care for pretty pictures, then go for Harper's. My instructor raves about Harper's, but ironically, has to use many other sources for his lectures and seminars. If biochem is not your "thing" to begin with, and you like subject material that is concise, well illustrated, and easy (enjoyable) to read, then choose Lippincott (and maybe buy a used copy of Harper's as a reference text, as I did).