I can't read an ungrammatical book. I'm angry at the writer, the publisher, the editor, the agent, and the industry by Chapter 2. The modern love of sentence fragments for no reason (it's not an action scene, it isn't internal dialog) particularly irks me. I have actually "heaved a book with great force" because of this and a few times posted a review about the ineptness to amazon.
I prefer plot and rising tension and so on, but if someone writes brilliantly I can read unplotted litfic, like Netherland by O'Neill or The Other by David Guterson, which did have a plot but it was oddly structured with the climax coming in the middle. Those are not my favorite novels; my favorites tell a story and don't let beautiful language get in the way of that. In litfic, Cold Mountain is a good example: beautiful prose, a lovely and moving story. In thrillers, Lee Child writes a terrific story and is a good writer. There are a hundred mystery writers who can do both. In fantasy, Patrick Rothfuss is just one example of a solid stylist and good storyteller.
I think I can tell when the author is in love with their own skills and that bugs me almost as much as ungrammatical prose. The language is in service to the story; mostly, it should melt into the page and leave only the story behind. Writing is about the reader's needs to be swept away into a fictional world, not about your own self-love and pride over your abilities. Writing beautifully but self-indulgently is like exposing your dingdong in the park and then demanding I say it was good sex for me too. It just wasn't!