^Its okay to when talking about the movie itself, but when comparing movies or talking about them as a whole, they shouldn't be sealed off in a little bubble of how they were at the time. I respect a movie like The Exorcist, but I wouldn't put it in my top horror movies, because it wasn't scary to me no matter how scared people were back 1973.
You're way oversimplifying it.
There is a difference between a movie that hasn't aged well (like Tron) and a classic - like the aforementioned Wizard of OZ.
There are all sorts of reasons why WOZ is a classic - for example the reason the movie went from black-and-white to color in the beginning is because in 1939 black-and-white was still commonplace, so the audience was tricked into thinking the movie would be in black-and-white. When the audience was then blasted with color during the dream sequence it really packed a punch.
If you don't know that you are missing a part of the movie, you are not understanding the full impact and emotion of that scene where Dorothy opens the door. It was basically the Matrix bullet time camera shots or Avatar 3D effects of it's time.
And if you don't appreciate WOZ then you will miss all sorts of references in later movies, references to ruby slippers, flying monkeys, and the iconic melting scene will go right over your head.
IMO it really is somewhat boorish to ignore the timeperiod in which a movie is made, you go right into the same category as mouth-breathing Michael Bay fanboys.