For me, I don't consider viewing a bad film (or reading a bad book, or watching a bad play, TV programme, etc) a waste of time. Why? Because as a novelist and storyteller myself, the study of failure is often as instructive - if not more instructive - than the study of success. It is never wasted time, for that reason, and I will always consider myself a student of good storytelling.

Granted, that isn't true for everyone, and as such, yes, it is better to be well-informed on if a film is worth your time. But I still don't think aggregator sites are the answer, as I said in my other comment. :)