I won't just give an EU to a review because it has pictures, but if it answers all of my questions and keeps my attention the whole way through I will. If it keeps my attention and answers most but not all of my questions, I'll vote Useful. If it can't keep my attention, I don't vote because it's not fair to vote on a review I couldn't read.
I vote EU if a review gives me a really good idea of what a product is like, especially if it answers questions I had. If I'm on the fence about buying something, a really good review should make up my mind. Pictures are great, but just having photos doesn't automatically equal useful, they should provide new info somehow.
An entertaining review is a nice bonus! I tend to be fairly wordy, so I try to throw some humor in when I can to keep things from getting too dry.