Good question and interesting thread IMO.
my 2cents:
TBH, I generally don't care too much what any reviewer says about anything. I will read/watch/buy whatever the hell I want and have long since stopped caring what some invisible person might say/feel/think. I ain't them, they ain't me and they sure ain't buying me the book/movie ticket/clothing/dinner/etc.
While a reviewer's opinion will not necessarily sway me one way or the other, I do enjoy reading amusing, literate, tongue-in-cheek writing that I feel doesn't patronize me or go out of its way to criticize the subject matter being reviewed. For most reviews, I tend to look for facts where possible [e.g. restaurant prices, movie lengths, excessive typos in books, etc].
I detest reviewers that try to come off as "the smartest person in the room" or who consistently ridicule the work of others in an effort to make themselves appear more clever. Really? You hated Matrix 2? Gee, let's see you do better - don't tell me...show me.
So, FWIW, I say be honest, have a sense of humour ahout things and try to be as objective as possible about the subject matter, all without trying desperately to be oh-so-clever.
Not giving away major plot points and posting spoilers is simply common sense and a matter of common courtesy to me as well.