I'm not quite sure about it, but I also think that the whole "if you cannot say anything nice, don't say anything" thing is very much an anglo thing.

Around here, Germany, art critics are celebrated for their often acerbic criticism. E.g. look for Marcel Reich-Ranicki on youtube, though I don't know if translations really convey everything properly :) Also, talking about the quality of anything isn't considered "intelligent" or "honest" around here if you don't talk about negative aspects. If you just say nice things, you are quickly considered dishonest, a salesman or dimwitted. Of course you need to state some valid-sounding reasons for anything negative, same as for the positive aspects, otherwise you'll be considered shallow or dimwitted as well.