It's lighter in weight than beech and generally has better aesthetic qualities. However, from what I've seen not all walnut is equal by any means. Some are not much prettier than decent beech stocks but, certainly from new, at least, there's a premium to be paid.
For my part, most walnut doesn't sway me into wanting to pay extra for it. However, every so often one will crop up and I'll find it so attractive I'll want to buy it even though I neither need the gun or can even afford to buy it. So far, I've always managed to resist the temptation.