After waiting for so long to finally get this book, I've discovered it to be well worth the wait.
Stephen Schwartz is releasing two versions of vocal selections for wicked, this version containing the melody interpolated into the piano part, and another book that is billed as a professional acompaniment without the melody necessarily built into the piano arrangement. This led many to speculate that the "with melody" version would therefore be much easier and less true to the music. Although I haven't seen the other book yet as it has yet to be released as I write this, you should definitely know that this book has not one "easy" arrangement. The arrangers have done a really excellent job of keeping the parts interesting while building in the melody. For instance, "Defying Gravity," the amazing Act-One closing number, is particularly well done, and if you can work through the key-- (it remains, as in the show, in Db) you will be VERY satisfied with the richness and fullness of the sound.
Schwartz has adapted the songs for use as solos or (where applicable) duets, removing longer instrumental breaks, trimming ensemble sections, and providing some new lyrics and endings to make the songs work really well for this new format. This in my opinion is yet another reason to purchase the book, as it gives fans of the show a way to interpret small sections of some of the songs differently.
Sometimes I do wish some cuts could have been avoided (notably I miss the wonderful "We deserve each other" theme that appears on the cast album intersecting "Dancing through Life" and the counterpoint melody "Who's that mage..." in "One Short Day"), but Schwartz is right, it would have impeded the creation of solo pieces to put those in.
The score for Wicked is definitely not to be missed, it really is a must have-- (especially while I wait patiently for the imminent release of the other version of the score!)
Overall, the music is wonderful, the arrangements remain challenging, but are extremely well edited and contain chord diagrams to help you along as well. Well done.