I loved watching this. First off it is an origin movie, I recall seeing this in the first run Digimon series. I love how it was expanded and explained how the main characters knew about Digimon in the series.
Animation was great! It was what I am in love with, old style animation. Bold lines, darker themes, and almost realistic art. Sound was great as well. No opening theme, but the ending theme is pretty good. In story music I feel like I've heard it somewhere else, just can't recall, but is also good.
Characters in this one I think interacted well even though it is only the digimon, and the brother and sister characters. I don't think anything really needed explaining, it explains itself, and I also already watched the initial series. If you just jump into this without watching the series though you would probably want more explanation on everything.
Overall a lovely watch and recommend it to anyone who has watched older anime and or anime movies.