I guess I should mention that I buy the books I'm reviewing here. No one likes my opinions well enough to ask for them on purpose, so you nice readers get what you get because I liked the blurbs or someone recommended it or... Something attracted me.
I'm kind of a butterfly when when it comes to buying, although I spend a little more money at Torquere because some of my buddies from a writing site publish there. Some Dreamspinner cause I like their website, and the other publishers' things I get from Fictionwise because I'm too lazy to set up accounts all over the internet.
What does attract me, aside from a juicy review or a rec from a friend? Sometimes it's a new story from a known name, sometimes the blurb (gotta love a well written blurb, it's like a quick condensation of the first quarter of the story and you HAVE to read more) or the setting. That isn't quite the blurb to me, that's just where I find out about the setting. If the setting doesn't sound like every other story in the genre, or a character sounds like he's got an interesting hook or a flaw, that will make me want to read.
If all of that stuff works out, I'll read most anything. I don't go looking for BDSM, but I've read stories with that that really worked for me, and others that were DNF. Paranormal, sometimes, we're back to that blurb thing, urban fantasy, science fiction, all good, contemporary, sure, bring it on.
The covers don't matter so much: the writers don't have a lot of control over that, although I click past some covers REAL fast. It's the words I want. Pick a good excerpt if there's going to be an excerpt, 'cause that tells me style and content. I read those before plunking my money down.