I was looking forward to this, because it certainly sounded ambitious and unique. It's an adventure film, fantasy movie, and historical action/drama film all at once, and was apparently made to commemorate 1000 titles produced by legendary Japanese film studio Toho. It's certainly an epic, maybe to its detriment, given it runs for just over three hours and it's far from the most consistent film out there to exceed that length.
If you can embrace or get used to the runtime, and accept that some scenes are more exciting than others, there are some good things here that ultimately make it watchable. Toshiro Mifune is the lead, and he's always great. There's a memorable scene where he gets to fight an 8-headed dragon, too, ultimately giving himself an advantage by getting all eight heads drunk on particularly strong sake beforehand.
That does play out as a fantasy/flashback/dream scene of sorts, though, and is one of several (these sequences are one reason why The Three Treasures feels so long and overstuffed, even if the scenes when judged on their own can be fun). The main story is a little more grounded, and follows a prince being sent on a difficult and multi-layered quest after he's accused of murdering his brother.
The movie is a lot, and it's possible to see how it would have been amazing as an event film for audiences back in 1959. Parts hold up decently well, some sequences are enjoyable, and Mifune's good in the lead role (the supporting cast is also generally pretty strong; plenty of recognizable faces in the numerous roles). But it's certainly not a great epic, and its unevenness means that for everything that works, there's usually something that falls a bit flat. It's able to be cautiously recommended to fans of classic Japanese cinema, but probably few others.
