I've spoken of my problems with sci-fi and fantasy before. Some works in these genres are, of course, worse than others, but...
"The Rules" - all sci-fi and fantasy involve some element that is different from real life. This element is a creation of the author, who may be impressively imaginative, and my reaction is to say "Wow, that's an impressive imagination this author has" RATHER than being interested and involved with the characters he's created.
There comes a time (and I call it the Mr. Lundie sequence - a Brigadoon reference), when these rules need to be explained to the audience. For example: "If you put this ring on your finger you will become invisible and quickly move to some place else. So, if someone's swinging a sword at you, that would be a good time to put it on. But do not keep it on for too long, because then you'll become evil and seek power."
While these rules are being explained, my eyes glaze over. I find rule-explanation very boring. Now, a good novelist often explains other things, the background of Jacobean society, for example, but these things, being facts, ARE interesting to me. A set of rules I'll never have to remember again once I put down the book - yawn.
Remarkably frequently, the author is inconsistant in the use of rules, or, late in the action, introduces a new rule that changes our feelings about what's gone before. For instance, our favorite old guru loses a battle and gets dropped into a fiery chasm. At that point, the hero sheds a tear, and we're all supposed to feel sad because the guru's dead. But wait, two hundred pages later, it turns out he's not dead. Or he still exists as a spririt, or a hologram, or some such thing. This is good news, I guess, but boy do I feel cheated for shedding those tears 200 pages ago.
It's said that if you're totally involved (as a reader or audience), you never feel "the hand of the author" but, instead, react to all the characters and their drama as if it is real. Sci-fi and fantasy are genres in which I have a hard time doing that, and am inevitably aware of the hand of the author, the person who made all these silly rules up in the first place.