TLDR: The movie does a great job of recapping the anime, but have no fear nothing important was left on the cutting room floor. Though the movie is a recap of the anime that had aired in 2017, the movie does a great job of bringing the entire experience together. With the inclusion of a brand new intro we get to learn a little more about the characters, I won't spoil who. The episodes were also edited together in a way where anything important isn't lost, but the slower scenes are cut away. One that comes to mind is the scene with Habo. Otherwise any otherchanges are along the lines of music, one of the songs is unique and I don't remember it being in the original anime, taking the place of Hanezeve Caradhina from episode 1. Speaking of music and sound, it was amazing to hear it in a theater with the surround sound. All in all, it was a pleasant experience, where both people who haven't seen the show, as well as returning viewers can enjoy.

Edit: The first movie also only spans the first 8 episodes with the rest to come in the upcoming movie wandering twilight.