This morning's incoming queries coughed up a query that was 690 words. I know because I pasted it into Word and clicked "word count."
None of 690 words told me what the book was about. None.
The letter was full of how this book would be promoted; how "controversial" was an understatement; how it will "provoke" readers. Well, it provoked me, but not in the way the writer intended, I'll bet.
I couldn't even tell if it was fiction or non-fiction. I certainly couldn't tell where it belonged in a book store; the premise of the book; what problem it proposed to illuminate or solve (essential for non-fiction) or anything other than the writer had no clue how to communicate effectively.
This, as you might suspect, is a recipe for instant rejection.
It's easy to get so caught up and familiar with your project you forget your audience hasn't heard ANY of it. You have to start with the basics. Tell me the category, and the problem if it's non-fiction. Tell me the start of the plot if it's a novel.
If you're wondering if this could apply to your query, ask someone who has never read your book to read your query. Then ask them "what is this book about?" If the answer is anything but "I don't know" you're probably ok.