This is an important distinction!
When I started reading about behavioral economics, one experiment in particular made a profound impact on my outlook: the experimenters presented the subjects with collections of posters ranging from fine art lithos to cute pictures of kittens and such, and asked them to rank them from 1-10, with understanding that they could take the top-scoring ones home. The experimental group had to explain their rankings, while the control group just had to sort them from favorite to least favorite. The "explainers" were much more likely to rank the cute kittens higher than the fine art, and six months later, the group that took cute pictures home had mostly thrown their away, while the non-explainers who'd taken home the fine art works had hung onto theirs.
In other words, the more art speaks to you, the harder it is to express what makes it so moving.
I do a lot of book-reviewing and I generally confine my remarks to the reasons I think you might like a given book — it's the way I learned to talk about books when I was a bookseller, because that's the essential service that a good bookseller provides: "If you buy this book, you'll find it enjoyable in the following ways. If that's your sort of thing, this is the book for you."
But sometimes I teach writing — about once every two years at one of the Clarion workshops — and that's where I have to try and figure out why a story is good, not just why it pleases me. In other words, to identify the elements of a piece that, if honed, replicated and systematized, the writer can use to make their future work as good as possible. This is the hardest part of teaching writing (it's much easier to identify the stuff that isn't working and explain why, but the universe of all the ways you shouldn't write is so large that it's barely worth charting — much like the universe of all the books you shouldn't bother reading, which is why I generally review books I can recommend).
Among Gaiman's many talents is an uncanny knack for explaining not just what he enjoys about something, but why he enjoys it. What's more, Gaiman's got incredible range: he explains what is great about books, sure, but also visual art, also movies, also genres, also people.
Gaiman explains what is great about things that aren't entirely successful, or are even objectionable. This is an especially impressive trick. Though the term "problematic" gets a lot of people's backs up, at its core, I find it incredible useful: things can be both pleasing and disappointing, can inspire you while still upsetting you, can be great with terrible elements. "Problematic" frees us from having to either pretend that the things we don't love have significant flaws, or that we don't love the things we love.
Gaiman loves some problematic things and people (as do we all), and here is where View From the Cheap Seats shines brightest: Gaiman tackles movies, books, and even people that, depending on the time and angle, are utterly reprehensible, or glorious. He neither sugar-coats nor condemns these contradictory beasts: rather, he explains how their contradictions are able to co-exist, and again, what makes them great, even with their flaws.
Jo Walton's utterly indispensable collection of book reviews is called What Makes This Book So Great, because that's one of Walton's catchphrases, and because, like Gaiman, Walton has the super-power of being able to tell you what you'll love about a book and why you'll love it (her Hugo/Nebula-winning novel Among Others is brilliant for many reasons, but most of all because her narrator shares her gift for answering the question, "what makes this book so great?").
I find it easy to explain why you'll like something. On my best days, with a lot of work, I can also tell you why it's great. I think you'll like Gaiman because he's entertaining and smart and insightful, and the reason why you'll find those things pleasurable is: he knows why things are great.
Speaking of great: I read Cheap Seats by listening to the audiobook, which Gaiman himself read. He is one of the field's great narrators (check out his narration of my story "The Right Book"), and the book itself is available as 15.5 hours of DRM-free MP3s from Downpour.com.
The View from the Cheap Seats: Selected Nonfiction [Neil Gaiman/William Morrow]