I just finished watching one of my favorite movies, Alien. I was thinking the movie could have probably ended after the ship blew up and it would have been just fine. But adding the final battle in the escape shuttle really added a great touch and made the movie much better.
Another is the end to Halloween. They could have easily ended with Michael Myers falling off the balcony, but the way they showed a montage of all of the locations that you’d seen in the movie gave it an extra eerie feeling.
An obvious one would be Rogue One. Fun fact: the escape from Darth Vader and tying it into A New Hope was not in the original cut. They added it after it was decided that ending with the planet blowing up was a little flat.
I can give you the exact opposite of what you are asking - a movie that was completely ruined by the gratuitous addition of a final scene.
There was a French-Dutch film in 1988 called The Vanishing that was quite brilliant. The ending was such a gut-punch that people left the theatre feeling shell-shocked. Few films achieved that sort of response (spoiler alert - the “bad guy” wins, in an utterly audacious fashion).
When Hollywood did an English language remake in 1993, they decided that Americans wouldn’t like a film with such an ending, so they added an extra scene that completely undid the entire premise of the movie, with a happy ending of the bad guy getting his comeuppance and boy and girl embracing like a teen romance. They took 3 minutes to destroy what the film had spent 100 minutes creating. WORST MOVIE EVER.
I just found out that the original cut of Alien DID end with the monster on the ship while Ripley escapes. Scott had asked for additional budget and filming time to add the battle on the aboard the shuttle.
Also interesting: what Scott originally wanted to do was to have the alien kill Ripley aboard the shuttle and then record something in the ships log mimicking Dallas’ voice. That could have been interesting.
