#1 and #2 have somewhat differing views on this topic.
#1 dislikes most sex scenes in most books and skips over them because they tend to be boring and gratuitous. The book would have been better served just closing the door before the scene occurred. #2 loves sex scenes and appreciates them way more, and never ever skips them.
However, occasionally a book will have a good sex scene in it. What makes a good sex scene in #1’s view is that it either drives forward character development or it drives forward the plot. A really good sex scene will not be identical for every character. The lovers will discover something about themselves or about each other, or the reader will discover something. It isn’t just sex!
There’s only one Georgette Heyer novel that #1 wishes had a sex scene in it, A Civil Contract. In it they have to have had sex, but how?
Good sex scenes: Freedom and Necessity had a fantastic true-to-life scene. One Good Earl Deserves a Lover had three really good sex scenes in it, each different and full of character development (and steamy!) Both of us love those two books! There are many others that aren’t coming to mind right now (the former is the first sex scene I came across worth reading, the latter is the most recent #1 has read). Mary Balough is pretty good at them too. I don’t remember which book it was, but there was a great regency where the hero kept asking for consent and the heroine kept giving it… despite what the Jonathan Chaits of the world would have us believe, consent is really sexy. #2 agrees and also thinks there are way more good sex scenes than #1 has found! But then again, I read erotica and slashfic, neither of which #1 reads.
Bad sex scenes: Anything non-consensual or that starts out non-consensual, especially if it starts out non-consensual (furthering the myth that she’ll like it once it gets started). This includes characters who are not capable of consent. Unanimous Ewwww. Any sex scene that could be repeated with any other pair of characters is also bad to #1 (but not as bad to #2)… the generic scene written without the characters in mind. And, of course, there are certain over-used turns of phrase that tend to make the reader giggle… that works if the sex scene is supposed to make the reader giggle (or it fits the characters’ thought processes), but usually it’s just a really badly written scene. Turgid! #2 wishes that men in sex scenes would quit laving everything. Find a thesaurus.
Readers, tell us the best sex scenes in fiction!