I think it's difficult to review Guardians of Oz fairly. The film is produced by Anima Estudios, a Mexican animation studio, and was released theatrically in Mexico and a handful of other countries before being picked up for distribution by Lionsgate and dubbed in English for release in the United States. Lionsgate's release does not include the original Spanish language track, which I think is a disservice to the film because I don't think much effort was put into translating the film to English. I can't say for sure that all or most of my problems with the film are a result of the translation, but being from Mexico and somewhat fluent in Spanish, I am disappointed that the only version of the film presently available to me is this one.
Much of the dialogue is awkward and poorly written, and it doesn't help that the voice cast isn't particularly strong. Instead of casting more "real" voice actors, someone (presumably at Lionsgate) opted to cast YouTube personalities Mikey Bolts and Jenn McAllister as the lead characters, Ozzy and Gabby, respectively. While I've certainly seen animated films with worse voice acting (I'm looking at you, The Patchwork Girl of Oz), I think having better voice talent would have gone a long way here. I actually don't mind the voices of the Scarecrow, Tin Man, and Lion, but I really feel like Ambyr Childers was miscast as Eveline. Granted, she didn't have much to work with given how bland and repetitive the dialogue is, but her voice just doesn't suit the character well.
The characters are designed by Jorge Gutierrez and his wife, Sandra Equihua, who also conceived the story for the film. Guiterrez is best known for directing the animated film The Book of Life, which I haven't seen, but there are obvious similarities visually between that film and this one. I think it's sort of an acquired taste, so I can see why some people are turned off by the look of the film, but I think it works, and I'm personally all for getting away from the traditional, typically MGM-inspired, depictions of Oz. As for the quality of the animation itself, it's not the best, but it's also not the worst I've seen (still looking at you, Patchwork Girl). Considering the film's very low budget, reportedly $4.5 million, I think the animation is fine and that it would be unfair to dismiss it based on its animation (which I know happens pretty often with lower-budget animated fare).
The general plot of the film isn't very original, but the film is short enough and paced well enough for that not to be a big problem. It is interesting to have flying monkeys, who we're used to seeing as just "background" characters, at the center of an Oz story, but I think the story would benefit from having a villain other than a resurrected Witch of the West. I noticed some similarities between this and Legends of Oz: Dorothy's Return, both in story and in design, but I'm sure that's just a result of working from the same source material and making a film for the same demographic.
Dorothy herself has only a very brief appearance in the film, and there are a handful of nods to the books and to the MGM film in there, which I didn't expect to see - mostly just "name-dropping" characters that Oz fans will recognize, but there's a cameo by a character from the MGM film that caught me off-guard and that I enjoyed so much that I won't spoil it here.
At the end of the day, I'm disappointed with this release, but I do think that it's worth seeing. If I'm ever able to see the Spanish language version of the film, I'll come back and review it separately, but I don't regret the purchase and I'm glad to have the movie in my collection. I'm not sure how to gauge the film's success in Mexico or internationally, but if the filmmakers were to revisit this world either in a sequel or a television series, I enjoyed this film enough overall to be up for that.
You can buy Guardians of Oz on DVD on Amazon here. It's also available on most streaming services to own or rent digitally in HD.