georgia, I think I have been put off by the commentaries/introductions, notes at the end, by having to read so many of them while studying English at school.
All our copies of whichever of Chaucer's Tales or Shakespeare play we were 'doing', even collections of poetry were overburdened with these notes and cross references.
It meant continually being made to stop and look up each reference either to find the meaning of the Middle English word or see what Shakespeare, Keats or Milton was alluding too in a particular passage.
I think there is a place for them at the end of 'learned works' if it will add something to you (the reader's) enjoyment or understanding, otherwise I feel they can bog you down.

Introductions normally contain spoilers. That, for me, is one good reason not to read them. I frequently go back and read them afterwards, and find they add some insight into what I've just read - but I wouldn't have wanted to read, for example, the introduction in my edition of The Turn of the Screw with its long discussion about the ambiguities about the book, before I'd actually read the story.

This caused me a problem once. There is an introduction to Life of Pi which I skipped - it looked like a "how I came to write this book" essay. Which was, in fact, what it was - but it was a fictional introduction, which was intended to be read as part of the novel....

I usually save the introductions for last, not because I care about "spoilers", but because I want to be familiar with what's being discussed. Nothing stands out in my mind though as being particularly good or bad.

Martin, my edition of War and Peace lists all the plot points at the head of each chapter. Does yours, and if so did it annoy you?

I do the same thing. Sometimes its enlightening, other times I get to the end of one page and realize it has nothing to do with the book I just read. My biggest beef about these intros is when it goes on for more then a few pages. Can't remember what recent book did this - but it was one I wanted to read. I got to page 10 of the intro, realized I had many more, and tossed it.

Disputantum - no, it's just got books and chapters.

It does have a useful list of principal characters, however, which I found myself referring to on a regular basis.

I hate reading introductions. As a Lit student I'm expected to and honestly I hardly ever do. Reading criticism on a text I'm about to read when I hardly have time to read the text itself makes me say, 'Nope, I won't be reading this intro!' Needless to say I don't read introductions in books I read for pleasure; the exception is Stephen King's 'Dark Tower' series. He writes on how and why the books are/were written - why it took so long to write them all, etc. It's very interesting to get some insight into an author's mind, especially when it's taken him 40 years to write the seven books in a series.