I would say there's not too much sex unless:
a) it's a genre where people want some story and there's so much sex there's no time for story - or build up of sexual tension
b) there's so many sex scenes it's getting repetitive and thus boring. Even if the physical act or position is different in the next scene, if it feels the same it might feel like a pointless repeat.
Either way, I think that comes down to bad writing more than a surplus of sex or different reader expectations due to genre. If there are so many sex scenes that there's no time for a story, then the story isn't well-written. If the sex scenes are repetitive and the story gets boring, same deal.
"It's a genre where people want some story..." -- That's really any genre, including erotica. Erotica still has a story, and other genres certainly have room for sex if the
story calls for it. I've written romances that had little to no sex, and thrillers that had a lot of sex. Just depends on the story. If I wrote a thriller that had car chase scene after car chase scene, to the point that readers were annoyed and bored, that would be a reflection on me as a writer and my story as a failure, rather than whether car chase scenes in and of themselves add to a story, get repetitive, etc. A story that has too many car chases, fight scenes, breakfast scenes, etc., is just as boring and badly written as one with too many sex scenes.