The story is vastly better than the movie. The movie makes no sense. She's shown being able to act in the present on future information. This rips the heart out of the story. First, she is now morally responsible for her daughter's death, which wasn't the case in the story. More importantly, the ability to act in the present on future information is basicly a superpower. She could take over the world, win every lottery and invest that money into finding a cure for her kid's disease. Instead she lives her life exactly as if she wasn't able to act in the present on future information. In the story she experienced all her life simultaneously. She was't able to affect the timeline. She experienced every moment of her life after she learned Hexapod B simultaneously, but could no more change her future than you can change your past.

I think this is something that really worked well in the movie, but takes a little more consideration after watching it because the movie doesn't really stop to explain this part:

Heptapod communication, and later on Louise, is performative. Imagine that you're playing a part in a live theater. You've read the script. You know what's going to happen next. You have lines to say, and you say them. You choose to participate in the performance.

It's a really interesting resolution to the argument between free will and determinism.

In this case, we can infer that, even though Louise knew everything that would happen, including her daughter's disease, she chose to play her role anyway. She understood that it was just a smaller part of a much larger, pre-determined script, and she was content to be an actor in it at all.

For another example of this being hinted at in the movie, Abbott knew exactly the fate that awaited him. He could have avoided it, but didn't. That was his role.

It's a metaphysical argument that's deeply unsatisfying to a lot of people. For a lot of folks, free will means being able to force change as you see fit -- the Edge of Tomorrow position. But, for a minority of others, free will and determinism can coexist if you're willing to accept that just because things can be changed doesn't mean they should be. It's the ultimate form of stoicism.

(Also not addressed in the movie is the neat question of whether the heptapods' original decision to interact with humans for the sake of their own future is part of the script, or if it was an action they took outside of the script for their own sake.)

I disagree extremely strongly.

I thought a lot of the tone, which made the short story so good, was lost, probably due to the medium and the audience. It became much more of a sci-fi alien thriller than a commentary on mortality.

I found that, having read the short story, I enjoyed the movie less than those who had not read it.

I have not read the story yet, so I can't comment on that part. I completely agree about the first half of the movie and that feeling of dread. What brilliant tension!

Why does that make it better?

The story is mostly two paper characters exchanging exposition.