I ran into one author around here where...
Well, the words were correctly spelled. The sentences were grammatical. Punctuation was where punctuation should be. The individual paragraphs mostly made sense. But they didn't string together into a narrative in any way I could put together.
Characters appeared without introduction. There'd be dialogue tagged with a name that had never appeared before, and I'd have no idea who they were or what they were going on about. Or a female character would walk in, and there'd be a description of her body and her wardrobe, but no indication of who she was, beyond eye candy.
Scenes jumped from one setting and group of characters (or group of inscrutable names and shapely thighs, anyway) to another without warning or notification. There was no indication of how the characters or events in one scene were linked to those in another.
Stuff happened without apparent cause or consequence, involving people that had never been introduced to the reader.
It was like the author didn't realize that not everyone could read his mind and know all the things he wasn't actually writing down. I tried two or three of his stories before I gave up.
They were harder to read than the ones where the author lives by Andrew Jackson's philosophy that, "It's a damn poor mind that can only think of one way to spell a word," repeatedly switches tense and person mid-paragraph, believes punctuation is optional, forgets their main characters' names, and writes sex scenes despite clearly being a virgin who failed Sex Ed (or took the conservative version - just say no).