One thing I'm noticing: a lot of times, high concept in contemporary means it's an adaptation or twist on a familiar story (ex-10 Things I Hate About You, Shut Out...), because that gives you an easy shorthand to explain it.
The other thing I'm seeing is a lot of books that engage some jarring issue -- and take it to the next level. BREAK is a self-harm book, but the kid doesn't just sit around cutting himself, he stages elaborate accidents with a very clear goal of breaking all of his bones. THE FAULT IN OUR STARS is about kids with cancer, but they don't just sit around having cancer, they traipse off to Amsterdam to get mad at their favourite writer.
See, to me, BREAK is high-concept but 10 THINGS I HATE ABOUT YOU or THE FAULT IN OUR STARS is not, and I think that exposes, just for me personally, how high-concept is not
just the killer one-sentence hook, but - like most things in writing/publishing - needs that extra subjective 'fizz' to qualify as high-concept.
For TFIOS - "Kids with cancer go to Amsterdam in search of their favourite author." In that specific case, the things that Sage mentions as the clear defining points of high-concept ("very easy to understand what the book is about in a simple description") actually work against it in this case. From that simple log-line, I find myself predicting that it will basically be a '10's version of A WALK TO REMEMBER, with a lot of romantic scenery porn, one of them dying tragically and a lot of philosophical musings on love, cancer and dying young. I haven't read it yet - don't tell me if I'm right.
To me, high-concept is when that outside-the-box one-sentence pitch makes you go, "I want to know what HAPPENS!" and, IMO, that word 'happens' is very important. For example, the much-quoted example of I HUNT KILLERS is basically the perfect high-concept contemporary hook: "the son of a notorious serial killer uses his inherited skills to find a copycat." Or BREAK - "a boy goes on a mission to break all his bones." When you hear that, you're probably not thinking, "I want to see if it has pretty writing" or "I want to see what the reviewers say about this", or "I like the author." You're just thinking, "I want to see where this goes." The PLOT is the main urgent factor that gets you wanting to read/see it.
So I don't personally think 10 THINGS is exactly high-concept because, although it does confirm to the traditional high-concept premise of "X means Y", I don't think it's that kind of "wham" in the stomach that makes you think "I need to see what happens" - because, odds are, the log-line has made you guess, because, odds are, Kate and 'Petruchio' (or whatever his movie-expy is named) fight, have conflict, get back together, kiss at the end.
Is it shock value? Maybe. But don't diminish the power of shock value. A true shock will never leave you and is a very strong accomplishment from any author.