Read the book first (admittedly, finishing it with only a couple of hours to spare before watching the film, and only having started because I wanted to've read it before said watching), and it's a darker, starrier thing than its cinematic adaptation. It sees Gaiman attempting, as is his wont, to create something deeply universal - archetypal - by deploying and reworking familiar elements and forms, seeking a synthesis between Story and Self-reflexivity to arrive at something both underlying and new; and, as usual for Gaiman's longer form prose, it shows occasional hints of being something special but never ascends to the heights to which it aspires. There's just something missing - I think that maybe the inversions and deconstructions of fairytale which structure Stardust, while lending the novel much of its interest, also undermine its central assumed narratival drives, without the text proferring a sufficiently satisfying alternative way of reading it.
The film, taken on its own terms (which are more modest), is more successful. It's definitely more whimsical in tone, and highlighted by a number of very pleasing performances (Claire Danes as Yvaine, Michelle Pfeiffer as the witch, Robert DeNiro's pirate (of course) and also the fellow playing Septimus, who reminded me of Steve Coogan); sets and special effects are appropriate (The Princess Bride by way of The Brothers Grimm, and it's appropriately somewhat askew, too, while always remaining entertaining.
(film w/ Michelle - who incidentally found it very satisfying)