Story: First off, this isn't really a movie. Its more a fifteen-minute short telling us how Digimon really started. This isn't the most interesting of the Digimon films. But, at such a short length I suppose it can't really pave way for a superb storyline.
Tai and Kari, only about 5 or 6 at the time of said incident, come across a Digi-egg. Soon to hatch from it is Koromon- but take note: This is NOT the Koromon from Digimon Series One what Tai befriends. This one is somewhat less intelligent, less friendly when digivolved and much more troublesome. Overnight Koromon then digivolves to Agumon, and, with Kari on his back, sets outside for a nice midnight stroll. Tai, worried for his sisters safety, runs outside to save her when an enormous Digi-Egg appears in the sky and out comes a giant green bird of a Digimon, what immediatelly goes for Agumon and tries to fight him. Digivolutions take place and so and so happens like you'd expect it would. The other soon-to-be-digidestined witness this event, what turns out to be the very event what leads them to becoming the chosen ones.
Animation: Not great. The people in this look sloppy, with exception for main characters like Tai. Sora, Matt and all the others looking at the fights from their windows really do look in horrible shape. All in block colours the animation is TOO simple, even for an anime of that time.
Sound: The soundtrack for Digimon is so cute <3 Its the same old songs as every show for this film really. Nothing new.
Characters: As much as I absolutely adore the characters in the original Digimon as if they were my own children, they aren't really explored in this movie. Tai is shown as a frequent joker who loves his sister and works hard to keep her in ckeck. Kari is shown as a cute little girl who quickly comes to love anything, including black fuzzy Digimons hatching out of weird eggs from an unknown destination. Like I've already mentioned, the other characters aren't really seen much so aren't really expressed very well.
Overall: If you like Digimon and want to know how the characters came to be the Chosen Ones then you'll find this an interesting short, but if not then this won't really appeal.