I'm not talking about a remake, let's pretend this film was never made in the first place. I think these days people like to jump in when they see a slight plot hole. I just dont think it would have been as popular.
Hard to say.
You have a point. With the internet now, people's opinions are easier to publish. Message boards, blogs, vlogs, twitter, whatever. Now anybody can post their opinion anywhere. And though I appreciate the irony of me posting this on a message board, the internet has led a lot of people to believe they're opinion means more than it does. It's not outside possibility you'd get people online going; "Why didn't Marty's parents recognise him at the end? Waaah! This film sucks."
Saying that, for the most part, Back To The Future is fairly tightly written. And there are massive blockbusters that are positively reviewed now. BTTF might still be popular.
Though, you'd probably get some morality group or another offended that Marty dates his own mother or some such nonsense.