I think for any "reaction" type video to be worthwhile and worth watching the subject has to have an extremely strong emotional connection to whatever they're seeing for the first time or the video needs to be insanely shocking - like the 2 girls 1 cup example.
Those Twilight ones were legit because those fans have an intense emotional connection with the movie. There are also some really good Star Wars Force Awakens reactions. These are legit and very entertaining to watch: https://youtu.be/3JcmEnmmkCA







