Hmm, if you want to speak genre, then speculative fiction appeals to me the most. Within it, dark fantasy > high fantasy > swords and sorcery > dystopian fiction >magical realism/slipstream/surrealism > soft sci-fi > general low fantasy > urban fantasy > hard sci-fi. But this is a /very/ general order. There are /plenty/ of urban fantasies that I love more than dark fantasies, so it really depends on the story.
If you want to get more specific with subject, here are some things I like (but again, they do not need to be present for me to like a story):
- A strong, clear, meaningful, but non-preachy theme. Favourites include one (wo)man against the world, the merits of revenge, the hollowness of perfection, the value of freedom, choice, standing up for what you believe in, whether you are wrong or right or even have a remote chance of succeeding...
- Something dark but strangely enticing (eg. vampires)
- Something light but not good
- Twists, especially if they're actually /meaningful/ and not just surprising (one thing that endears me to O. Henry's writing)
- Complexity, be it in character or plot
- Good ol' action. With /tension/. "funny" fight scenes don't appeal to me at all, and even darkly humourous ones would need to be really good to please me.
- Emotional reaction to/in said action
- High stakes > low stakes
- Scenes where many/all characters get revealed to have extra layers of depth. Reveals of The Past, villains showing emotion, heroes turning dark, ect. are all enjoyed.
But ultimately, I care much less about the subject than about the story. If you have a rounded, changing, larger-than-life character I care about (extra points if they're tragic, flawed, yet cool), then I'd forgive the story even if it were set in high school with the main plot revolving around a humorous drama (probably my least favourite setting/subject/concept).