Words.
Salis, have I got a book for you! Just let me get it published...
I like good prose quality. It doesn't have to be poetic, but I like a good natural flow and a certain elegance. Clear and simple is good. Purple or clunky is bad.
I like a really good story. If it makes me laugh or cry, so much the better.
I like some depth, some sense that the author has some wisdom, compassion, exceptional understanding of the human condition.
Imagination, a sense of wonder, delight, intelligence: those are also pretty cool.
I know this is all kind of abstract, but that's why I tend to read quite widely. I'm not interested so much in a particular genre (although SFF has always been a favourite) as I am in the best of each genre. I like the cream.