This movie is ment to serve as a reboot from the original series and it is the first movie from the three that are planned to release.
This movie covers up the first half of the series it not just does that but we get a bit of background of the characters like Renton's dad Adrock Thurston and more of how Eurleka was familiar with holland and the rest. We also learn a bit about Charles and Ray Beams renton's temporary foster parents.
In terms of the original series I have only watched the first half of the series so far and because this movie does that as well. I just thought what difference does this movie have and it gives more background about the characters. Which I suppose when I continue watch the orginal series they might cover more on later but I have to wait and see.
Some people may see this as a reboot but other could see it as a spin off to the original which is how I see it. It is up to you on how you want the see because if it was a reboot they would have changed the animation, changed the voice actors and possibly restarted the series from scratch all together.
But I am not sure on how anime reboots work so do bare with me.
It might not be as good as the original series but from what I have it is pretty decent. I can't wait for movie two and three to come out.
Also thank you Funimation for casting Fred Tatashiore as Renton's dad I hope you bring more inion/non anime voice actors like James Arnold Taylor, Jeff Bennett and Dee Bradley Baker in your anime dubs.