This is going to be one of those discussions isn't it?
The problem is that there are two different things here: 1. Direct Personal Opinions: I like this, I don't like this. Those are as they are and it's unlikely anyone is going to change them. However, there's also 2. Quality. This is much more difficult because it does not just depend on opinions but on understanding the 'language of film' technical and emotional, having the patience to go beyond simple and immediate reactions etc. etc.
So someone has every right to think that Citizen Kane is boring (and they can't be 'wrong' in that), but that doesn't make Citizen Kane a film of low quality or cultural worth. There's too much about it that is technically and dramatically brilliant. Those things will never persuade everyone to enjoy it, however.