Miss Snark, what is it with editors saying they love you, love your writing, want you, would like nothing more than to publish your next book, but don't like your current idea? I thought it would end once I had my first novel published, but it hasn't and I'm getting a bit sick of hearing this. Is it that they have a fixed idea in their heads that you should be writing something in particular, or is it just another one of those 'let her down gently' phrases?
This is the part of the industry I hate a lot. It happens more than you think. That it happens at all was really horrifying.
"I love your writing but don't like your current idea" can be just that. I've got a couple people who've queried me with probably three novels at this point now. Great writers. I just hate the book. It's usually too violent or icky or has subject matter that I find gross. So I say "love your writing, hate this book, got anything else" and they cough up another novel, and I read it. This can go on for donkey's years I think.
Now, the other part of that is when an author published a book and we're working on the second one. This only seems to happen when the second book is optioned of course. The writer goes completely off the rails and writes a book that is near and dear to his/her heart. It's completely different from the first novel. We all love the writing and hate the book. Trust me, these are NOT happy conversations and threats of death and dismemberment are whispered far and wide across the landscape.
My point of view (biased of course) is to suck it up and write something your agent loves. You probably should not follow this advice quite as closely as I want you too cause I have a greedy little mercantile heart and my reaction to "but this is my art" is "art fart, gimme something I can sell, the dog needs a new tam".
Yes publishing is a business but the product can't be measured by a simple yardstick. Would that it could; widget production sounds mighty good some days.
So, take cold comfort that you're a good writer. And don't plan for this "I love your writing but not your idea" to ever disappear. Sadly, it's a fact of life. And as things go, it's probably better than "you suck, go develop an interest in the aerodynamics of kites".