I came across this series via Pinterest, and The Wood Between the Worlds was the first to arrive via inter-library loan. This isn't the ideal place to start, of course, but I couldn't resist. Deborah Maze's pictures are lovely, evoking Pauline Baynes's original illustrations and also adding an ethereal twist of her own.
The Magician's Nephew doesn't work exceedingly well in picture book form. This volume cuts off at a very awkward spot (right when Jadis enters Polly and Diggory's world--picture books shouldn't have cliffhangers!). One of the many joys of the Narniad is how well it works for young readers, especially as a read-aloud, and I can see The Wood Between the Worlds used to supplement such a reading, since the pictures are so rich and evocative. On its own, it lacks a certain coherence, and all the charm of Lewis's narration is absent from the brief text boxes. While The Lion, the Witch, and the Wardrobe gets a four-volume picture book treatment, The Magician's Nephew only gets two books, so I know the next one leaves the story unfinished. The Wood Between the Worlds could also be really fun to flip through while listening to the audiobook, so it has its uses--but as a standalone book, it doesn't really work for me.