Saw Alita last night. I'm going to keep the spoilers light, but if you've read any of the manga you'll be fine.
As you can imagine, it's a pretty Westernized version of the actual story. And it went through the normal contortions of turning an animated feature into a film adaptation.
But my sister, no fangirl of Alita or anime in general, loved it. So I can say that the contortions were probably effective at getting bodies into seats.
As an anime adaptation, the comparatively short length forced a lot of changes.
As initially reported the story gets as far as the beginning of the Motorball arc, but they really contorted the chronology of the story to make it happen, and Alita's 2nd League debut happens while Hugo is still alive.
Makuku ends up being squashed together with at least two minor characters to give us the sewer scene with the grind cutters - and they've left off the colliseum entirely, so Makuku doesn't have Kinuba's giant body (they made the grind-cutters the weapon of a minor Motorball player that Hugo's gang targets at Vector's request). While they still relayed Makuku's story about being abandoned in the sewers, its so rushed that most of the pathos is lost (in no small part because he lacks the maggot body). Cameron tries to make us pity the guy during the fight the way we did Makuku, but it's a pretty hard sell when he looks so much more normal.
Vector, Ido, Alita and Hugo all survive as characters pretty much intact, albeit with some obvious changes (Hugo is depicted as being in his early twenties, etc). They played up Vector's villain status, and Alita kills him after Hugo dies (so the later subplot with Kaos to build a tower to Tiapheres will have to change - if they make it that far).
Jennifer Connelly plays a character who only appeared in an OVA - in this she's Ido's estranged wife, and Alita's initial body (which does have the flower engraving on the arms) was originally intended for their deceased daughter. She works for Vector as an engineer for Motorball players (his primary business in this version). Ido's Tiapheran mark is gone in this version - he says he removed it himself - and honestly it makes sense for the adaptation, given that Jennifer Connelly's stated desire to return to the floating city and the fact that she still has her mark. It would spoil the reveal of Ido's origins.
The one thing I have a hard time forgiving is what they've done to Desty Nova. His screentime is pretty minimal, but they've decided to make him a much more serious villain - neither flan nor his maniacal laughter have made an appearance yet - and there's been no talk of karma or the nature of humanity or sanity. I'm really going to have a hard time accepting this version of Nova going forward, if James Cameron makes enough money to justify a second film. He's even still in Tiapheres, and he's already as powerful as he was in the early stage of Last Order.
The acting is pretty decent - apart from some understandable awkwardness around Alita's green-screened face, and the few extremely Western filler scenes thrown in are forgivable.
The berserker body has some of the later Imaginos functions - nanotech, but not the chameleon ability - and they've also made given damascus blade Martian origins... and in this version Alita steals it from Zapan during the scene where she damages his face. Zapan's character is handled pretty well, but I think the obsession he has towards Alita doesn't translate well for a Western audience.
Ido's assistant isn't Mr. Gonzo - initially I thought it was supposed to be Tanya, but it's just a random hefty black actress they shoehorned in. I don't know much about James Cameron, but this might actually have been a diversity thing - the only other major black character is Vector, who is one of the bad guys. There was nothing wrong with the actress's performance, but she was completely forgettable, and the conversation that Ido has with Gonzo about the berserker body instead happens with Alita.
Also, in this version Alita goes to the crashed Martian ship and takes the berserker body from it, instead of Ido having done it years earlier and putting it into storage. There's some weird addition about Alita's cybernetic heart being special Martian tech that allows her to interface with the berserker body - I think it was an unnecessary addition, but it's forgivable.
Christoph Waltz is an amazing actor, but he really should have been Nova - he plays a whimsical villain far better than a heroic character. I have to assume he didn't want a background role. He's also pretty old by now, and it was really hard to buy him as a hunter-warrior given how awkward the rocket hammer design they went with was. It looks quite like some of the more "realistic" versions I've seen people make on Youtube, in fact, and it really didn't seem to add much power to his strikes (like the ones on Youtube).
A younger actor, or a sleeker design (one more faithful to the original) would have worked much better.
Separating my love for the source material from the fact that it had to be changed for the new medium, I'd give it a 7/10.
Far, *far* better than every live-action anime adaptation I've ever seen, and by a wide margin. It might have been better if it had been made by Marvel Studios, but it would also have been butchered worse than the people Nova kidnaps.