Thanks so much for mentioning that very real "bad day" issue. I suspect it's especially problem with movie reviews, because--as another commenter has said--you typically see only one screening.

With books, if you get an advance reader's copy weeks before the pub date, you can avoid it by going back to a book or giving yourself time to think about what may have been a too-hasty first impression. But movie critics don't have that luxury. Their job is a lot harder than it looks.