There are many reasons one would want to attend an opening night showing of any movie. These are mostly based on the amount of people that attend a given movie on the first night it shows, so YMMV.
For most people, the effect of a crowded movie theater induces excitement, and for some this is indeed an adrenaline rush, especially in a stadium-seating theater, where you have more of an idea of the level of crowdedness, and the sound of people talking to one another isn't as dulled by the seat in front of them. The noise level, the close quarters, and the relative lack of light, combined with a decent picture and loud sound all help one loosen up and have a good time.
I've personally noticed that, especially in stadium-seating theaters, the perceived adrenaline level in my bloodstream seems higher and constant. The added bonus of being among the first people to see a movie in the country makes opening night more exciting for most.
I've seen Spider-Man, Star Wars: Episode II, Murder by Numbers, Harry Potter and the Sorcerer's Stone, and The Matrix Reloaded on opening night, if memory serves. All of these movies but Murder by Numbers was much more enjoyable opening night than any other time I viewed them after the release date in theaters.
At the opening night showing of Spider-Man, I was sitting in the Regal Cinemas Hollywood 20 near the mall, and the excitement level was high. The stadium-seating theater was packed, this was a big-name big-expectations action movie, and everyone was hyped and ready. The now-requisite five minutes of advertising was shown, and the previews rolled, and as the Columbia/Sony Pictures intro music was fading out, a low rumbling noise could be heard from the middle of the front row. It happened to be the loudest fart I think I have ever been witness to, and it could be heard echoing throughout the entire theater, laughter coming next, making the first 25 seconds of the movie inaudible over the noise, but nobody cared. It just added to the effect.
Then there was the Star Wars: Episode II opening night, where someone behind me tried and failed to open a bag of Reese's Pieces, instead causing the bag to explode, and candy to fly everywhere. He then offered everyone around him the former contents of his now-empty wrapper.
It's important to remember, however, that if you're one that is easily annoyed by other people inside a theater, you're probably not going to enjoy opening night as much as those who thrive on that sort of atmosphere. It's one of those things that some get and some don't. See a movie when you enjoy it most.
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