I love science fiction book cover art. Liking any individual artistic style is subject a personal taste. One of my favorite cover artists is the award winning John Picacio who does a lot of cover art for Pyr.
One of the reasons I like physical bookstores over online ones is because cover art is more easily browsed that way. Locus Online does an admirable job showcasing a year’s worth of science fiction/fantasy book covers side by side, but rare is the online bookstore that does this and I still want the bigger images without having to use the slower method of the click-through.
According to poll SF Signal did last year, only half of respondents said they purchased a book solely on its cover. That surprises me in that people would base a decision on that alone. Sure covers matter, but I find a bad cover drives me away from a purchase more than a good one will ensure it.