1. It really is more like the pilot for a TV series than what I typically think of as a movie. Mostly because a 80-100 minute movie should have more closure than a 80-100 minute TV arc. We still don't know:
A. Who is Alphamon? What's his deal? B. Why does he care about Meiccomon? For that matter, we know hell all about Meiko and Meiccomon, besides 'shy transfer student/Chosen Child'. C. Why did the Digital World close off in the past? Why is it re-opening now? D. Why introduce the 02 kids in such an ominous way, then never even mention them in text beyond a shot of the Men in Blacks' computer showing their location as Unknown. Considering Miyako and Iori are Takeru's neighbors, Daisuke looked up to Taichi, all three attended school with Takeru and Hikari (though Iori might still be in elementary school), and they are generally shown as friends. I mean, I can interpret plenty of sinister reasons, but they didn't even hang a lampshade on it.
I guess I feel like a movie in a series should be more stand-alone. But as a TV series, this works for me. Especially since the first arc is 'getting the band back together', a well-worn trope.
2. I like Taichi's arc, though it could be clarified a bit more. He's starting to wonder if the shounen mentality of 'punch it until it stops moving or becomes your friend' works in the real world, where there's things like collateral damage. And putting 'two-time shounen hero' on his CV isn't much. Basically, he's starting to grow up and wonder about things that he couldn't focus on when he was an 11 year old trying to protect his friends and sister in a scary alternate world. (Someone compared it to Mimi's arc in Adventure, except I don't think it's the same motivation. Mimi was pretty sensibly scared at all the shit they had to go through, and so didn't want to fight. Taichi was thinking more about other people, especially the normal humans that get involved when you have monster fights in Tokyo. And about how people don't care that Kuwagamon started it when they see it and Greymon both knocking over buildings. it's not resolved, but Taichi does affirm that the time for long-term questions isn't when you need to get the giant monster away from the civilians and novice Chosen Child.
Actually, a lot of the characters had growing-up arcs. Jou was Mister Not Appearing in This Movie because of his need to get into a good college. Takeru and Jou got teased about love interests (I don't care about Takeru/Hikari as a ship, but I will endorse them being the cutest friends).
3. Back in the fandom heyday, Meiko's very announcement would get her branded as a 'Canon Mary Sue'. Because she fits a lot of the tropes self-inserts do: new female Chosen Child, potentially plot-relevant (though Hikari fit these in the original series), and the same age as Taichi and Yamato, for maximum shipability. (I probably would have been in that, despite not being much of a shipper for the 01 kids.)
Now, I'm torn between 'good, boost that gender ratio!' and 'dude, Digimon, you had trouble with 8 kids and their mons, don't add more'. Also 'wouldn't it be funny if Meiko was Jou's mentioned girlfriend'. Because I appreciate an economy of characters.
4. Thing I am wary about: the show turning into the Taichi and Yamato show. Like so many other versions of the franchise does with the hero and rival -- aka the ones that don't just have three obvious leads. It's early, so maybe the other movies will let other characters take the lead and get to save the day. And get new Mega/Ultimate/whatever-the-high-one-is for their mon (which I guess Patamon and Tailmon have, but this time, let them use them). Actually, now that I think about it, why didn't the other kids go to Perfect/Ultimate versions of their 'mons? I thought it was the same reason they couldn't in 02 until Gennai unlocked them, but then Taichi and Yamato are all 'oh, let's try Omegamon'. (Unless Agumon and Gabumon can only briefly pass through their higher forms on their way to the scary fusion trump card.)
I did like Sora and the rest of the cast being 'we are locking you in a ferris wheel car until you get over yourselves, bye now'. Everyone had cute moments. Especially Mimi, who sees a giant monster attack as the chance to make sure everyone gets presents from America.
I pick a lot of nits here, but that's mostly because I had fun. So I do a lot of thinking about 'what next' and speculate about the directions I'd take things.