Since the site is still undergoing the phase where some definitions are not clear, there can be some questions about which it may not bel clear if such questions belong or not. I would thus propose that if someone votes to close a question he would write the motivation in the comment, if it's not obvious (like question being duplicate and duplicate linked - then of course it shouldn't be reiterated by every voter). I don't know if there's a way to remind people about it, etc. but it is really frustrating when question is being voted to close without any indication what the voter things is wrong with it.
Yes if something is not obvious we should leave comments why a question is voted to close.
If a question is postet like this:
"What is your favourite X"
Isn't it obvious that this is a subjective question? So i vote to close those kind of questions and propose to make a community wiki and rephrase the question.
"Who is your favourite Female Sci-Fi Author?"
rephrase the question to:
"Who are some good female scifi authors? [Community Wiki]