Here are two things that very few people should ever attempt in novels: genius characters and descriptions of sex. Someone who is not a genius cannot write genius. I think that if I were a writer I might - might - be able to write a side character who was a genius by describing as exactly as possible the two geniuses I've known in my life. (What's that, Pete? Oh, sorry. Three. Three geniuses. Thanks, Pete.) I don't know that I could write that character as saying very much, but I could describe how s/he sat while watching TV or eating steak. But I would never - in a million years! - attempt to write, a) a first-person novel about a genius, or b) a novel where one of the main, speaking characters is a genius. This is one of my major criticisms of The Di Vinci Code: there wasn't a single "puzzle" in that book that was in the least bit difficult to solve. And yet the characters - one of whom is a genius cryptographer, the best in France!, and another of whom is a genius "symbologist" ::grumblegnashhiss&spit:: - were totally mystified! Here is the deal, Authors Of The World: if you are not a genius (and please, seek outside verification on this, and not from your mother), and you can figure out the solution to a puzzle you have created, then Q.E.D., it does not take a genius to figure it out. And it's insulting to your reader to imply as much!
And the sex thing... I cannot think of a single book in which I've read a really detailed sex scene and thought, "Man, now this is art!" But I can think of plenty of times when I've thought, "Man, now this is embarrassing!" Here are the books that spring immediately to mind where this phenomenon is concerned: Clan of the Cave Bear, Jean M. Auel (and any of the sequels, for that matter; I've heard Plans of Passage is essentially pornography, but I couldn't even make it through The Mammoth Hunters); and The Mists of Avalon, Marion Bradley (and any of the sequels or prequels). If you have read a truly beautifully written sex scene in a book, please suggest it! But if tongues swirl anatomy in moist detail or ladies that are just deep enough for their lovers' giant johnsons, I will seriously question your taste.
The book I'm currently reading (The Historian) violates both of these precepts (or "fiats," if you prefer). There are no puzzles, but the side characters make very prosaic observations about things historical and the main character frequently comments on how he is "astounded" by the "quickness" of someone's mind, the "breadth" of their "intellect," or their "genius." And while one reference to a sex scene is very tasteful - more like a movie montage of provocative images - the other is a pseudo-sex scene (in that sex doesn't actually result) and involves "adolescent fumbling" and an "ugly white brassier." I mean really! It just leads me to believe that the author has never actually had sex and has never seen a movie with a rating higher than PG-13. And that makes it embarrassing, the way fan fiction is embarrassing. It's like a window into how she wishes her 16-year old life had been, or how her first time with her True Love had been/would be. And I don't need that window, because it's not an autobiography; it's a work of fiction with sci-fi/fantasy overtones that seriously stretches the limits of my suspension of disbelief.
Anyway, The Historian is like 600 pages long, I'm on page 444 and I've just been tearing through it (because the story is more interesting than the writing is bad/embarrassing, even if it's a stretch) so I've been thinking about this a lot. I have a high tolerance for crap: I read all but one of the Ender's Game sequels. (If that offends you, I... wait, no. I don't apologize. If that offends you, you enjoy bad novels. Sorry, but I'm pretty sure this is empirical truth. Okay, okay... Ender's Shadow wasn't so bad. Geez!) And I read a ton of Star Wars novels and a lot of fantasy novels, and let's face it, many of the latter are soft core for geeky adolescent girls. "I am a witch who rides a unicorn - don't fondle my heaving boozums, Mister Night Elf! Oh, your tumescent manhood - I mean elfhood - is too much for me! Make me a woman, sexy mythical creature! Take me now, before my unicorn gores you!"