I've had an ed say she loved the voice, the plot, and the premise but not the dialogue. There were literally all of three lines of dialogue in that ms.
Yes, here's an example of wanting to give feedback and avoid the problem at the same time, which editors ought to know are mutually exclusive goals. Sure, editors are sometimes skittish about approaching the problem, since some of the things you definitely can do while giving feedback are confuse, anger, frustrate, and offend people. Still, if you're going to skip the problem, skip the "feedback". This sort of letter just makes people wonder what you're using for brains.
"the writing is thin"
This most often means the writing didn't have enough color or personality of its own. This doesn't necessarily mean you need more description, though writers are frequently in danger of taking it that way. Good, muscular writing knows what its goal is in the manuscript, and gets it done with few words. If you choose the right few words, the right few telling details, you only need a few.
"it's too quiet"
This is a topic problem; the editor is saying there isn't enough of a hook. There are now so many books on the market with lovely writing and illustration that those facts alone will not sell a book. If the writing or art is breathtaking, then that can be a hook of its own. Otherwise, the book also needs to be about something people know they want.
"not substantial enough"
This could mean "too thin" or "too quiet" (see above). Hard to say which.
I have a friend who just got a rejection from an ed who said she loved the concept, loved the genuine voice, loved the really great writing, but rejected the ms b/c she wanted to see more b/w 2 characters. As writers we hear over and over that plot can be fixed. But believable voice, solid writing, original concept, etc...have to be there first. So what was the deal-e-oh here? Not even a revision request. Although she did ask to see anything else of the writer's. Is there a subliminal message, like, "I adore this, but my publisher will never green-light this project," huh?For writers, these kinds of rejections are both exhilarating and excruciating.
Sounds like a letter I would have ended with a revision request. It's sometimes hard, though, to be sure a writer's able to change a manuscript the way you think it needs to be changed. And while we'd love to give people the benefit of the doubt, we see a few hundred manuscripts every year that have distinct strengths and that are simply not ready to be published. If we gave all of them an open door for resubmission, we'd regret it almost instantly. My advice: think hard about this feedback, and if you like it enough to make some real changes to the manuscript, do resubmit it. And submit it elsewhere. And keep submitting.
My husband has noticed that I get more vague yet personal rejections of the "I loved this, really enjoyed it, want a copy for myself but...no." variety between May and September... Even worse are the friendly, unsigned replies from publishers who told me not to include a SASE b/c they only respond if interested... so someone actually SPENT MONEY to send me a vaguely polite rejection..His diagnosis? Summer Interns.(Though I half-wonder if the polite rejection from the "only respond if interested" publisher was, in fact, a veiled attempt to say "please don't EVER submit to us again." Then I stop being paranoid and make another pot of coffee to make me feel better...)
I would attribute any rejection in the vein of "This was so great! I can't think of a single thing to criticize! Not on your life!" to interns.
The friendly, unsigned replies from houses who don't promise a response, however, I would take as actually friendly (while obviously not real personal or helpful).
Now, I do know what you mean about a polite letter that was sent in the hope that the author would never submit again, but you can be absolutely sure you've never received one. You seem perfectly sane. We don't send those letters to the clueless or the people who need to work on their manuscript some more. We don't even send them to the people who we feel could really work on their writing some more. They are solely for the very occasional certifiably insane person whose manuscript and/or cover letter actually scares us. They are "Oh my god, send this person a very nice but vague letter and let's hope the next thing we get from him isn't a bomb" letters.
So far we have not gotten any bombs, but trust me, some of the slush is just that terrifying.