I won't comment on the quality of the writing, as many other reviewers have voiced their opinions on that subject, but please be aware that this collection only contains about half the illustrations from the books as they were published in their single-story form. Since it is the pictures rather than the words that appeal to the younger reader (and, I suspect, most of the older readers too), this is not the money-saving opportunity it may appear.
I had purchased one of the individual books and enjoyed it very much with my 2 year old daughter, so decided to purchase this collection to get the rest. I found it much more wordy since there is now twice as much text per illustration, and it is less appealing to its intended audience because of this imbalance. Avoid this edition and buy the single books (or get them from the library!)