There's actually a point I wanted to add to the discussion concerning 'older' movies. I think context is relevant but only to a point. I think there are movies that succeed in being 'timeless' which means they tend to be great no matter when you view them.
To me, 2001 is one of those movies. It was made 40 years ago but I don't perceive it as dated and don't feel the need to tell myself when this was made to be able to consider it a great movie.
Other movies include (for example) The Great Dictator. I still find that highly enjoyable today. It's a tremendous movie as it is. Put it in context and it's even greater but it's not even really necessary in my mind.
Other 'older' movies, however, just don't fare that well, in my view, anyway. And I think part of it has to do with the fact that some of the ideas and social concepts of the time were, plain and simply put, stupid. One of the things that always strikes me is the role of women who are very, very often (especially though not only, I must sadly say) reduced to nothing more than the source of a problem, something needing to be saved or a love interest for somebody.
I can enjoy movies like that because I'm aware of the time(s) but it really pretty much keeps me from considering them 'truly great' movies.
I realize that this is a bit of a slippery slope since times have changed quite a bit and not just in comparison to the way things were 40 or 50 years ago. So, you might ask, what about really old paintings or writings from several hundred years ago? Those times and social conventions are very often even more removed from today. I don't really have a satisfactory answer to this. There are works where it bothers me just as it does with the movies and others where it doesn't. I suppose it's not always completely rational.