Basic errors in punctuation, which, I'm sad to say, I see too often, and not just in self published books.
Lack of research. There's no excuse for it these days, when everyone has the internet at their fingertips. If you're writing about members of the nobility, find out the proper way to refer to them.
Attempts to write accents. Lots of apostrophes to represent dropped 'h's and so on is just distracting.
A weak central character. The central character should be the one driving the action.
Ttbb, I'm interested that you suggest 'too much dialogue' as a pet peeve. What do you consider too much? I like writing dialogue, and don't like to have too long a stretch without any. I'm always looking to see whether a scene can be improved by adding some. That said, dialogue must have a purpose, of course - to move the story along, or reveal character.