Many books catch my eye due to the art. Sometimes it is beautiful, sometimes evocative and sometimes horrible (see "Necromancer" and other Brian Lumley books for examples).
Otherworldly places suddenly come to life, ideas are given form, a vision in the imagination graces the cover. There is a delight in looking at art, Gibson's "Burning Chrome" is a true favourite, which simply invites the reader to open the book and dive right in.
Then there's artist interpretation which almost does a disservice to the work inside - "Fighting Fantasy 2 - The Citadel of Chaos" is a fine example of rather unusual art. Again, interpretation is everything.
The art on the book, "Journey to Infinity: Travels in Time", in the link is intriguing, it offers the reader a glimpse into the book yet tells nothing. Rather clever."Journey to Infinity: Travels in Time"