I would like to state first and foremost that this is an extremely important anime historically. This was one of the first theatrically released feature films from Toei Animation. It was also one of the first colored anime features films. The impact that this film had on anime as a whole is huge. That said, this film has not aged very well.
The story is all over the place. It takes forever for the main conflict to get started. First we follow some woodland creatures until one of them gets killed. Then we follow Sasuke as he goes to train and learn magic. Then there's
something about bandits. And then the bandits disappear for a bit. But then by the time Sasuke's done training, you've forgotten why he left in the first place. Then we have to worry about his sister that got kidnapped. The pacing is inconsistent, and conflicts are thrown around until you forget about earlier ones. Also be careful of which subs you watch. Sometimes the subs are flat out wrong. Even with my limited Japanese, I could tell that certain phrases were incorrect. This can lead to further confusion if you can't catch the errors.
The art on the other hand is the best part of this movie. The character designs suffer from weird anatomy and creepy faces. You could tell they were trying to copy Disney, while still making the film "Japanese." However, they hit a slightly uncanny valley in that regard. It's not too bad. But it does take out some of the immersion in some scenes. The animals on the other hand are done very well. The backgrounds are also nice. I absolutely love the way the animation things like fire, teleportation and liquid.
Another highlight of the film. Aside from some inconsistent lip sync (which is more an art problem than a sound problem) the sound is integrated very well into the film. The voice acting isn't anything to write home about. But things like whip cracks, lightning and other sound effects are very well done. The soundtrack is appropriate and well done.
The characters have little to no character whatsoever. Sasuke is a generic determined boy. His sister doesn't even have a name (or at least in the subs I saw she didn't.) The prince and witch are generic as well. Oddly the side characters have more character than most of the main cast. There is a side plot about a girl that won't leave these two bandits alone after they stole her trunk. That plot point gets forgotten about. But the lengths the bandits go to try and make her go away were entertaining. The girl however was annoying as hell. Most of the animals have their own quirks. But it's not enough to carry a whole movie.
In spite of this movie's flaws, I did enjoy it a bit. There was a final showdown between the witch and Sasuke that was very well done. The bandits and girl side plot was funny, even if it never got resolved. There was a scene involving a deer trying to follow Sasuke that I liked. There are things to enjoy about this movie. If you are an enthusiast I could see somebody being mildly entertained. The film is also made more fun by trying to point out all of the Snow White and Sleeping Beauty tropes that were probably being borrowed in this film.
Like I said before, this film is historically important. If you are a film historian, then this will not be the worst film you've ever seen. However, this movie still has not aged well at all. You could tell a lot of effort was put into this film. And in some areas like animation and sound, that hard work has paid off. I just wish more thought was put into things like pacing, character and story.