It depends on the film, really. There are some films that, when watching them, you know that nothing like this would ever be made today, and it just makes you appreciate them even more. Ghostbusters and The Evil Dead are perfect examples of this.
On the other hand, there are plenty of things out today that just never would have worked in the past. The Avengers, for example, probably would not have been nearly as good as it was had it come out 20 years ago. And films like Cabin in the Woods or Rise of the Planet of the Apes are essentially love letters to films that came before them, and would have never been made or appreciated without the films that came before them.
Really, I prefer not to think of films as "old" and "new", or "modern" and "dated". I just prefer to watch films. We, if they're good, anyways. Time of release or type of effects doesn't mean nearly as much to me as the script, the characters, and the overall story of the film.