Caution spoilers ahead

I'm a book review reader. Not just reviews of my own book, but in general. Reviewers are, of course, a generally intelligent bunch of individuals, no matter whether they write for a published journal, a blog, or simply post on a retail site or on Goodreads. I usually find reading their thoughts stimulating and enjoyable.

Here's one thing that I've always appreciated and respected in book reviews: the convention of marking spoilers as such, and even hiding them from view unless someone chooses to click on the jump/link/hidden text and read.

Because if reviews really are for readers, as they're supposed to be, it's a bit rude to just come out and say [spoiler ahead! highlight to read!] BRUCE WILLIS WAS DEAD THE WHOLE TIME, right?

Regarding SANCTUM, like many books, it has an ending that's unexpected. Many readers have commented about it in very general terms, and I love that. And I'm grateful that they let other readers experience that same thing for themselves.

What I don't love: A review that flat-out says (without the spoiler warning) something like: "At the end of the book, Malachi and Lela [highlight to read] come on now, people. You didn't really think I'd tell you that, did you?!? And that's how it goes."

(To be clear: I'm not talking about one review of SANCTUM in particular, and not even only about reviews of SANCTUM, just using it as an example)

But anyway, to all reviewers out there: I adore you. And I respect your right to do what you do. If you feel like your critique of a book would simply not be complete or coherent without revealing specific details of plot twists, etc., go ahead--just mark them clearly! [If revealing the details isn't necessary for the review, may I suggest you leave them out or speak of them only in the most general of terms?] It gives your fellow readers the choice--whether they want to be spoiled or not. It's the polite thing to do.

</rant>

 What do you guys think of spoilers? How do you define "spoiler," and what kinds of things should be marked as spoilers? What can be included without that kind of warning? Laying out the ending is obvious (or should be?), but what about all that stuff in between? And--do you read spoilers? Do they enhance your enjoyment or ... spoil it?