The Original Ending

Nice sexist point of view....

The ending makes much more sense than the original. It explains how he was able to walk around and do/know things that Sean Fentress had no knowledge of. How would Sean know where the bomb was or that the bomber left his ID on the train on purpose or that he knew the license plate of the van? Also, what's the point of sending an email if it's only a simulation?

"original"

I struggled with the parallel reality thing myself. Think about the time he got her off the train and she lived. How could she be in an alternate reality? That version of her was still part of the "reality-reality" of the people sending him back. Yet, they told him that she had been killed in the blast even though they insisted that she died. In the "alternate reality" ending he proved that people in the alternate reality can communicate with the reality-reality. Email is capable of travel from one reality to another? Way too much of a stretch without any bother of an explanation how it is accomplished - or at least an acknowledgement that the laws of physics would somehow permit it. Without an explanation the two realities would be running concurrent to each other. To me this meant there were now two copies of her walking around and they would both try to conduct the one life.

It's a little like the remake of Stepford Wives. The wives flip flopped from being robots to being real women with brain implants. In one scene they would be doing total robot things such as the ATM and boob inflation scene. Then they ended up being still alive without so much as a modicum of attempt to explain it.

Fatal Attraction is another movie with a changed ending based on test audience reaction ... why? Because, originally, he was arrested for the murder of Alex and everyone thinks the poor man has already been through enough already. So, they shot another ending where Beth gets to blow Alex away.

That's disappointing. I was so annoyed with the ending of the film, and now it feels even shittier than they had this better ending beforehand.

I wish when studios were pressured like this, they wouldn't be come up with something so absurd or saccharine or both. Reminds me of how at least when 28 Days Later was pressured into making a happier ending, at least the ending still fit in with the film (and still had an edge to it).

This was just a fan-edit, like the alternate "Dodgeball" ending where the bad guys win:

https://www.youtube.com/watch?v=RX1zEY0LIXQ

(although the "Dodgeball" fan was Stiller himself)

The original screenplay always had Colter survive his body's death:

https://www.actorpoint.com/movie-scripts/scripts/source-code.html

No “alternate” about it.

Besides which, as other posters have pointed out, it’s not just a “happy ending.” It’s a plot-critical confirmation that source code DOES create alternate realities, which is the ONLY way to explain how Colter can explore places that Sean never visited.