The general story was good, just good. But this is a Digimon movie and it dropped the ball with being that. Fans want to see new digivolutions and forms, exciting battles and team work! Most of the times they digivolved were entirely pointless, especially looking at you Ankylomon just stay in the car its faster! Not a single new digivolution despite having the opportunity, Angewomon was already evolved and Angemon could technically become an ultimate so at least could've done a DNA with Ankylo and Aquila for fun but no knock Angewomon out of form so Gato can DNA. The one "battle" the movie had was largely just there so they could check it off the list and it wasn't even a sweat for them, lasting all of two attacks. The movie does a complete overhaul of the franchise lore, digivices weren't what tied a digimon to a digidestined - its what allowed the then to channel their emotions to enable digivolving! So what, now they can't digivolve? They also wrote in the perfect way for the original tamers to get their digimon back and proceeded to say that's a terrible idea. If you liked the main 02 cast, get ready for them to be sidelined for Lui and Ukkomon!
Removing Digimon from the equation, as I said it was just a good average story. Its start was slow and Lui often flip flopped between hating digimon or wanting to reach out to Ukkomon, it can be chalked up to being a complex character or bad writing to move a story forward. The middle of the story where we see Lui and Ukkomon in the past is the movie at its more traumatizing but best, my only issue with this small portion was that it was such a sudden 180 tone shift with no lead up or hints. The ending was easily the worst part, as it doesn't actually give a valid solution to those experience similar abuse - just talk to them? Yeah that's cause for more abuse by calling them out on it.
Lastly, there is debate if this is a time travel movie and the director is incredibly vauge about it. He says it started that way as a time travel mystery but changed. When reviewing the events that took place, this was not time travel. If the end when Lui "changed" the past caused him not to meet Ukkomon and thus digidestined to never happen then when they come out of the dream state/past the events happening should not be happening. If you say well that just created another timeline and they return to their own, well then the digivices should still remain in tact and the newly hatched Ukkomon they were talking to in that "other timeline" wouldn't have knowledge of the events happening in Lui's timeline - it was HIS Ukkomon he was talking to in that dream state. Thus not time travel.
In summary, the concept of meeting the first tamer is cool but the execution was terrible.