I've always found written erotica more of a turn on than the visual.
When it comes to fantasy what I like most is the forbidden. Good people trying and failing to resist temptation. Doing bad things because it feels so good. Specific themes include incest (mother-son, father-daughter), happily married people cheating and age difference (late 30s-late 40s with 18-25 year olds).
I don't like characters who dive in too easily. The harder they resist the better. I like it when conscience and temptation enter into epic battle with the devil on the character's shoulder eventually beating out the angel.
I also prefer stories that focus on the before and after just as much as they focus on the sex itself. How the characters succumbed to the temptation is important. The sex itself is important. But I don't like stories that end with an orgasm. Explore what happens next. Characters dealing with the guilt, overcoming it and the continued sneaking around to continue their forbidden affair. To me a story is incomplete unless it deals with all three phases.
P.S. Fantasy and reality are two different things. I don't condone incest or cheating in real life. Leave it on the page.
