If you love a movie that much then it's one of your all time favorites. Doesn't matter when you watched it or when it came out.

That being said, I like to give movies at least a year before make my true assessment of them. I typically get 'theatre hype' where I come out of a movie pretty psyched about what I just saw. I'm a person who tends to like everything while he's watching it because I'm easily entertained. Only months later do I realize how crappy the movie was. That's how I felt about The Lost World, Daredevil, The Phantom Menace and many others. But for movies like Iron Man and The Dark Knight, even a year later I still wanted to see them again and when I did I liked them just as much. So that's how I knew they were great movies, and up there with my favorites.