This is very common among all fandoms, really.

It's very annoying to read a story that's been badly written (no shit Sherlock). Grammar and spelling are VERY important, but it can also just be how well the story flows and how exciting it is. I always recommend reading through your drafts again, because the events can go very fast and you might feel like it's at normal speed, but your readers will probably feel too rushed.

Remember, they don't know anything about your world, story, characters, etc. yet.

I think this is becoming too helpful.