Sex is like video games. It involves a lot of repetitive action which may be very enjoyable in real life, but writing about it in detail can be duller than dirt. I find that in order to make it interesting at all, one has to build up to it, give the players some personality, and include some atmosphere. It might be romantic, dangerous, awkward... just make it so there's SOME kind of emotion in the scene outside of sexual pleasure. If you have a sex scene it needs to be written very differently depending on circumstances; the reader should be able to tell by the descriptive action, dialogue, and general atmosphere whether this is a husband and wife of thirty years enjoying a second honeymoon, or a college student giving his landlady sex instead of rent money. In other words, the sex can't just be about the mechanics of sex! A good scene will include emotional responses, character idiosyncrasies, and perhaps even a bit of humor.
Because I never miss a chance to self-promote, I offer this example from my story
It's Good to be the King, where the protagonist ("You") is
about to have sex with a young woman who is not only virginal, but also somewhat naive about what sex even is. Her invitation is phrased as, "Will you... will you be with me now, as a man with a woman?" She doesn't know quite how to put it, only that she wants to do what she's seen men and women do from a distance. As the scene progresses, her actions and what she says continuously drives home the idea that she doesn't really know what she's doing; she's offering trust and looking for guidance, and when she feels her first orgasm she's completely overwhelmed. Everything about the scene is driven by her character, and thus it is very different from scenes elsewhere in the story where the women involved are more experienced and confident. And that, I think, is what can make such scenes more interesting to write AND to read.
That having been said, I agree that the rest of the story is much more interesting for me to write.
One other thing I like to do with my sex scenes (and this is controversial around here) is to use illustrations. I do try to make it so the scene works entirely without them; the pictures are there to supplement the story, not to tell it. But I think if it's done right, a picture can say a thousand words.