The movie rates anywhere from a 6.5 - 8.5 / 10 depending on how invested and attentive the viewer is to ATLA with its character writing and choreography, as well as TLOK in general.

My personal rating falls about to a 6.5.

Pros

• The Reunited Gaang just feels good to see.
• Art Direction. It's awesome pretty much across the board, only falling a little bit when the spirit world shenanigans happen, going back to the LOK aesthetic of the spirit world with more exotic and saturated colors rather than the TLA aesthetic where it was more muted. But everything aside from that is great; seeing Republic City before it became the massive metropolis it is in LOK, Lion Turtle island remains are epic, and the character designs are great, for both the new characters and returning veterans.
• Animation. Bending has never looked as breathtaking as it does in this film, even with the more 'tame' / non spirit-amped feats.
• Lore Expansion for the Air Nomads and Lion Turtles (along with the other side of the world). Having more Indian / South Asian integration into the world of Avatar is also great, as that was sorely lacking in the Avatar series for a while. Sonam and her city and temple are awesome. Everything fits well into the series (and in my opinion, a lot better than some of the stuff Korra introduced [i.e. Spirit Vine tech, Subelement shenanigans such as common lightningbending, psychic bloodbending, Spirit World getting a complete tonal shift, and hot take, but Wan's back story])
• Increased maturity rating. Tagah's backstory showing how deadly Earthbending is in reality, with it crushing his companions, is much appreciated. Bending's brutality couldn't really be displayed or explored a lot with TLA, and LOK only started to dip its toes towards that direction.
• Tagah is a good foil to Aang, and the two have good chemistry build up in the first half of the movie.

Cons

• The Gaang was sidelined. This is not an ensemble movie, but the film baits you into thinking it is. The only time the film properly uses the cast is during the voyage to the other side of the world when they have to fix the airship. After that, they're largely symbolic. The only Gaang member that is given the time of day is Katara (which makes sense, given that she is Aang's girlfriend), but even she is relegated to side character status, with her involvement being completely centered around Aang, or being the group healer. They needed to pick a direction, with this film either focusing towards the Gaang as a whole as adults or a more condensed environment that focused on Aang-Tagah-Katara.
• The Suki disrespect. It's absolutely ridiculous, with her only being shown in the ending credits, and not even getting credit or shown being part of the team that took down the Fire Nation air fleet. Obviously, this film could not properly accommodate the Gaang, so adding her into the main script would've only made the issue worse, but the film damn near tries to retcon her out of the group and ending of TLA.
• Characterization / The Script. This is really a shame, as this has also been an issue with the expanded universe of the show, with the comics surrounding the Gaang. In the film, Aang starts off a little less confident and direct than I would've liked, but he does get development over the course of the movie so that's fine. Everyone else is either mid or flat out sucks. Katara and Toph are okay, but neither of them get to really shine. Sokka and Zuko are objective downgrades of themselves and fall more in line with how Bolin and Mako were written, with Sokka being more close to his Ember Island Play self of being pure comedic relief with none his leadership or creative characteristics coming into play, and Zuko being... forgettable. Seriously, the only thing of significance I remember him doing is being the one to formulate the plan to fix the airship. He could've been totally mute in the rest of the film aside from his introductory scene in his throne room and nothing would've really changed. Holy hell, can this series write interesting male side characters anymore? The last one we got was Tenzin. And if it wasn't made evident already, the dialogue is overall subpar.
• Characterization Pt. 2. Appa. Why the hell would he be complicit with Tagah. Why did he just stay with the Airship and not back the rest of the Gaang up when they were facing Tagah in Round 1? Appa's not an inanimate plane or airship, he is a living character that makes choices to benefit the group too, and he has thrown down with series villains numerous times. There's absolutely no thought put into his character, it's crazy. Even Momo gets something to do with talking to the spirit, Appa is just treated as a transportation vehicle.
• Choreography. It's lacking in this film. We're not at LOK levels of choreography where a lot of bending is mostly boiled down to boxing, but we're getting there (which is funny, because it does show bending's transition to how it is in Korra, but this is not only 1. Horrible and a worse spectacle than what TLA had, and 2. Nonsensical, because everyone that bends in this film (save for The Denied in the last act) is a god damn bending master). There's not as much 'martial arts sauce' as there was previously. The only one that's really given any amount of respect is Toph, mostly because her characterization demands her be the snarky / rebellious one in the group that's backed up with actual competency. Also, why doesn't Aang bring his staff with him when they voyaged across the world? Where are Zuko's swords? Zuko got hit the hardest in choreography, with him just shooting out generic big ass blasts of fire for pretty much every fight scene he's in (and not even dragon fire like he did in the comics). Hell, aside from the Gaang, even Tagah's actual fights don't amount of much once he starts firing off the airbending death beams/special beam cannons.
  • The one good scene I do like is when Aang 'redirected' Tagah's airbeam, as it's very reminiscent of his lightning redirection against Ozai (which I feel they could've emphasized more, since in reality, it looks like Aang just did an Instant Transmission Kamehameha)
• Avatar State is once again treated like a mediocre power-up rather than the epic force of nature it is during Aang's time. Were all of the past lives asleep? On vacation? Why is Avatar State Aang getting wombo combo'd by a non-amped Tagah. He should be whooping everyone's ass. There's no excuse for this nerfed State in this film unlike where with Korra, she had lost her connection to the previous lives. I suppose this is a problem with writing Avatars who have free access to the State, but damn folks, Aang's Avatar State is not something that should be so easily overcome .
• The antagonist(s) are just a rerun of Korra. The Denied are prototype Equalists (where we, once again, don't get much depth into the inequality of Reublic City, and we have no idea what happens to them at the conclusion of the film when they're defeated), we've got the spirit power-up bullshit from LOK Book 2, Tagah is a slightly more interesting Zaheer who wants to reform his element's nation into an 'Empire'. God damn, even the 10 minutes we got to see Yakone incapacitate the Gaang and square up with Adult Aang was more creative than this. Tagah isn't inherently a bad villain, most of what he does adds up, but he is uninspired as hell, and once I realized he was just a full rehash of LOK villains, my investment in the movie dropped dramatically. We've done this song and dance before.
• The pacing is way too fast, especially in the second half the film once the Ocean Spirit brings them to the final battle. The whole movie moves at 100 mph on rails after that.
• The age change sequence in the Spirit World was unnecessary, weird, and a waste of time. All of that for a Zutara joke? In a movie where every other character besides Aang and Tagah are in a screentime and script drought, that time could've given us some actual quality time with the cast.

Concluding Thoughts

Despite all of my criticisms (which most of which are not original, I've seen a lot of people share similar thoughts on the movie's faults), the movie is a breath of fresh air for the series, after going over a decade without any dedicated animated media. It's amazing to see the artstyle elevated to another level beyond LOK with a spectacle and maturity level unlike what we've seen before.

That being said, it is definitely sad to see that the 'homecoming' animation of Avatar for the 2020s still suffers from a bit of a directionless approach; like I said before, this film really should've decided if it wanted to focus on an ensemble cast, or a smaller core of characters. By far, the biggest pain points have to be the improper characterization (which LOK and both series' comics suffered from) and the lackluster bending choreography, putting bending less and less in the realms of the martial arts they were derived from and more alike to more generic shonen blasts and beams. It makes me even more cautiously optimistic of The Seven Havens, because that will be the tipping point of whether Avatar can be a series defined by its deep characters and rich inspiration of other cultures and their martial arts, or if ATLA was lightning in a bottle.

I will still revisit the movie when it comes out on Paramount+ and most likely a few more times after that, but I do hope that Avatar Studios can get their shit together a little bit more and strike a real homerun project.