Let me start out by saying, as a fan of Pok?mon since the beginning, I love this movie. It tells an original interpretation of the beginning of the Pok?mon story, mainly Ash as he is just starting out. I found this to be a great interpretation of the source material with an original story and enough fan service for fans that have been there for 20 years without being too reliant to be open for younger viewers. I especially love how it touched on how magical the world of Pok?mon is with the normal school dream. It's not perfect, but it's pretty awesome.
Now with this, I've read multiple negative reviews across the web and I think people are going in with the wrong mindset and as a result are critiquing it based on things it wasn't trying to be in the first place. First, I'll address some "this isn't exactly like season 1" criticisms. The largest complaint I hear is "Misty and Brock only appear in the credits and not in the main movie" and "they replaced Misty and Brock with new companion characters." While I admit I would have liked to see them in their gym leader roles like Brock did in Origins, I think many people forget that we're currently in season 21, and Misty hasn't been a companion since season 5 and Brock hasn't been a companion since season 13. All the other characters you see in the credits are the other companions Ash has had. I don't blame them for having different companions.
Another criticism I've seen is "Verity and Sorrel don't get enough development." Historically the companions haven't received a lot of development in the movies. Tell me, what did Misty do in Pok?mon the first movie, what did Tracy do in Pok?mon the Movie 2000, what did Brock do in Pok?mon 3 the movie? I can only recall Misty getting some "shipping development" in 2000, that didn't last in the main series. They received some pretty good development if you ask me, considering it's a 2 hour movie.
Another criticism I've seen is "Charmeleon/Charizard isn't a jerk to Ash." That's because Ash is far more competent in this movie. Charmeleon/Charizard didn't respect Ash in season 1, because he was pretty incompetent. In this movie Ash may not completely know what he's doing, but he learns and remembers.
There are many similar complaints about how it's not a "shot for shot condensation of season 1," and to that I must ask "do you really want another Last Air Bender?" Then there's the other main criticism I've seen, the "it's as if this was written for children" criticisms. Things such as "the story is too simple," "things get solved too easily," and "they're really doing the chosen one story again?" To which I say "it's not Wolf Children, and it's not trying to be Wolf Children, it's a Pok?mon movie." You need to remember who the target audience is. While there is a lot to love about Pok?mon as an adult, and this movie does have a lot of fan service for the fans that have been there since the start, Pok?mon is a franchise that primarily is targeted to children. Toy Story is a very simple movie that tells the story about 2 toys that got lost, have to escape a toy torturing child, to get back to their loving child before he moves. It's a simple story, because children won't be able to follow a super complex story (and is pretty complex considering the other movies). Of course things get resolved simply, kids like happy endings. You can do the Don Bluth "take children to difficult places, but you have to end on a happy note," with emphasis on "end on a happy note." Yes, Ash dies to come back to (which I saw coming with how they were setting everything up), but he had to come back because of the "end happy." Kids don't want to leave depressed. They're doing the chosen one again; yeah, that's what these movies do. Ash is the chosen one. It's like complaining that Star Wars is about Jedi.
I'm not saying this movie is immune to criticisms. The Pikachu talking thing, while touching, was very out of place. The "Bye Bye Butterfree" arc didn't have the same weight as it did in the anime. Raikou's inclusion didn't have any other purpose than "we included the other 2 legendary dogs, we need to include the third." I rated it 8/10 for a reason. However, if you do review this movie, I humbly ask that you consider what it was trying to be, because it's not fair to rate a slasher film negatively because the teen couple that get killed in the first 10 minutes didn't get enough development.