You wouldn't be able to eat popcorn, drink a coke and watch the movie at the same time.
If the popper was popping corn, and they were selling a candy bar, the movie would pause.
They would announce that the next versions of the movie would enable colour blind people to watch in colour, and the deaf to hear it.
The film would break every 15 minutes and in the most important parts.
They would announce new breakthroughs in movie technology - colour and sound - forgetting that most other movies have had these for years.
Every new movie would require a new projector.
The projector would claim to take 32mm in film size, but in reality it would only show 16mm magnified to make it look like 32mm.
Every movie would look pretty, but actually have mishmash holding it together, and contain no plot. Ooops! Sorry, that's from the "What if Hollywood Made Movies" list.
They would promise you an action/adventure flick starring Arnold Schwarzenegger and Sandra Bullock, but it would be 3 years late and end up being a sappy love story with Jim Carey and Madonna.
Their projectors must have reset buttons, requiring you to start the movie over and over to have any hope of seeing the entire film.
640 seconds? Whose gonna watch a movie longer than that??"