Alright just saw the movie. As a big time fan of the manga, I'm going to nitpick/criticize how faithful this is as an adaptation:
Changes I liked:
-Ido being a father and husband. This change was the best thing for the character. In the manga, he almost had a lover/almost daughter like obsession with Alita. Here isn't as creepy or ambiguous.
-The integration of motorball is doing more smoothly here. Smart move doing parts of motorball early. And it makes sense later how Alita leaves Ido to do motorball, given it was Hugo who introduced it to her in the first place. It's something to remember him.
-Finding the berserker suit in the mars craft is a fine change. I would have prefer that or how Ido has it collecting dust in his basement.
- The explanation and use of the big eyes. One of the first things I criticized when I saw the trailer. But I've gotten use it and wasn't a big problem. The explanation given is that cyborgs from mars all have that feature. It's unique among that world. Still I would prefer the big octopus lips myself but the change is fine.
Changes I didn't care for or meh on:
-Hugo. The worst criticism about the movie and it's justified. Look in the manga, Hugo was a street rat, a hoodlum, but he had a dream of reaching Triphraes/Zalem because that was his brother's wish. He became obsessive over it. To the point where he would literally climb up to reach that city in the sky. At that point, he lost any sanity he had after losing his body. His love for Alita was a superficial and immature love at best. His love for Alita, in this movie, was played too straight, too pure and wasn't shown how immature and shallow it was. Hugo was too clean and pretty boy in this movie.
-Scrapyard. Oh excuse me, I mean Iron City. I didn't like that change that much honestly. I would have liked for them called the city the Scrapyard like it is in the manga. Speaking of the city, boy does that city look pretty clean in comparison to the manga. This is a city that has literal trash dumped on it daily. It supposed to be grimy and dirty. Speaking of grimy and dirty.
-Let's talk about PG-13 rating for this, shall we? Well I couldn't determine if the rating is so much a good or bad thing. One hand, the most visceral parts of manga/OVA in but didn't show any guts, brains, or eyeballs exploding all over the screen. They cut away from the dog getting sliced in half, which I'm fine with since I'm a dog lover. But boy does it feel like they were for a R rating without going the extra mile for the movie. I really wished they would have. Also I know it's more marketable as a PG-13 movie.
-The villains. Nova and Makaku/Grewishka . Makaku is supposed to be a parasitic maggot cyborg that has a liking for brains. He becomes obsessed with Alita over the course of their battles to the point that he decries his love for her. At one point it's noted that he was a patient of Desty Nova. Desty Nova doesn't even have any type of confrontation with Alita until the 4th or 5th Volume of the manga. So in comparison, here Grewishka does a worm like body. But he isn't a psychotic or deranged. He's being manipulated by Nova. But in manga everything he did was of his volition. Nova, in the movie, is some sort of grand mastermind and ruler of Zalem, I think? And while it's true he is a mastermind of sorts but he's more aloof and crazed than he is in the movie.
-Other things. Alita still has her berserker body at the end of the movie. Doesn't make sense if you make a sequel. She is supposed to give her berserker body for motorball because it was a combat body and it wasn't compatible for motorball iirc. The fight in the office was good but I still prefer how was in the manga between Makaku and Alita in the sewers, Makaku's home. It plays into the relationship between Alita and her villains. They changed Jashugan who was black/darkskinned to Jai Courtney. Yuck.
As someone who thought this movie was going to fail in every aspect, I did like it. A lot actually. As far as westernized adaptation of an anime/manga goes, this is the best you're gotta get. I feel like if they went in on it being a hard R and gritty up the city and characters. This would have perfect imo. But as it stands though, I enjoyed a lot. They animed the fuck out this which is good. They even had Alita say HAI YA before hitting Grewishka. It was cringy but I like it. Alita is the best thing about the movie. Alita will always be one of my favorite characters of all time, manga, anime, or movie. She's a bad ass female character that needs to be celebrated. 8/10.