"My novel is War and Peace, in space!"
"My novel is Charlotte's Web, with vampires!"
In other words "my novel" is the retelling of a now-classic work. I get a lot of these, and while Charlotte's Web with vampires is a total non-starter for me, the others are not. I'd keep reading.
All too often however, the query doesn't tell me what I really want to know: what have YOU added to the story? How have you built on the work that's come before? How is your book better, faster, stronger, smarter, newer, zippier, than the classic upon which it is based.
Think about Romeo and Juliet. The musical West Side Story is R&J, but set on the west side of New York, during the influx of immigrants from Puerto Rico. The story isn't about family rivals in this case; it's ethnic rivalry. It says something about the melting pot we like to think America is. It says something about the American Dream for people coming from distant places. On top of the R&J love story, there's a cultural commentary.
That's what I'd need to know if you're querying West Side Story.
If you're having a hard time figuring out what you added to the story, you're not ready to query. "Catcher in the Rye set in the present day" isn't enough to hold my interest. Holden Caulfield as a transgender
**see Laina's comment at 11:49 for for strikeout revision.