What if a platoon of G.I.'s from the Japanese army were to be send back in time 400 years right in the middle of the feudal wars that led to the formation of the Tokugawa Shogunate? Great pitch right? The movie does exactly what it says on the tin.
Thankfully the writers didn't bother to explain the, usually ridiculous in sci-fi movies, scientific mumbo jumbo of time transport. No how's or why's. They just did. However the time transport sequence itself is trippy as hell and quite beautiful, if not a bit dated. Not as silly as one would imagine.
The rest of the movie follows the premise to a T. But while it loses a bit of steam with the various subplots that follow the G.I.s arrival to medieval Japan, it picks up with a devastating battle sequence. Undoubtedly it's the main order of the day. The whole concept and by extension the movie itself, was probably originated from this simple pitch: what if G.I.'s equipped with the latest in modern warfare were to fight samurais? And boy does it deliver.
The main battle sequence that spans more than half an hour is probably one of THE best of its kind in 70's action/war movies. Not only is it relentless and exhausting in pace and length, it's also a terrific mish-mash of styles and techniques that only unique premises like G.I. Samurai can deliver. I mean, where else would you get the chance to feature tanks, ninjas complete with shuriikens, a helicopter and samurais in the same shot? The G.I. platoon led by lieutenant Iba tears literally through hundreds of extras, gunning them down with machine guns, mortars, grenades and tanks.
This mish-mash of styles is with one foot firmly rooted in the sprawling jidai-geki epic of Kurosawa's Kagemusha or Hiroshi Inagaki's Samurai Banners, while the other is in western action and war movies. There are stylistic touches (like the wonderful slow-motion shots and bloody violence) that bring Sam Peckinpah or Enzo G. Castellari circa Keoma to mind. Japanese cinema has always been influenced by westerns and other Hollywood works and vice versa, and G.I. Samurai effortlessly turns this east-meets-west melting pot into an exciting film.
The film-makers thankfully take the whole thing seriously and the movie benefits immensely from it. Not that tongue-in-cheek mentality is completely absent, it's just that it doesn't try to pander to so-bad-it's-good audiences that enjoy laughing at their movies. The budget was probably hefty, as it is evident in the hundreds of extras, elaborate costumes (very decent for a production that is not a traditional jidai-geki) and special effects. The camera-work and editing are all top notch, almost better than a movie with no higher artistic ambitions deserves.
It's not withouts its flaws either of course. There are many "song" scenes, where all sorts of 70's Japanese rock, disco and country songs play over montages (there's a bonding scene, a love-interest scene, a "war is hell" scene etc). The songs themselves are pretty lame and corny and detract from the whole thing. Although it clocks at a whooping 140 minutes, it flies like a bullet for the most part. Still some scenes, flashbacks and subplots in the first half could have been clipped for a tighter effect.
The cast also deserves a mention, featuring such prominent names as Sonny Chiba, Isao Natsuyagi (Goyokin, Samurai Wolf), Tsunehiko Watase (The Yakuza Papers) and Hiroyuki Sanada, all of them hitting the right notes.

I've seen about four other Japanese horror films and they weren't too impressive. However, I could sense that there was a sensible script guiding the way.
Not here, no way. This is about a detective who is trying to tie together similar murders that have been happening. When he finds a suspect to question, the suspect freaks out because they keep seeing a ghost. Then, the ghost starts to follow the detective around FOR A REASON THAT IS NEVER EXPLAINED AND TAKES UP MORE THAN HALF OF THE MOVIE.
Bad enough? Oh no. The film keeps switching perspectives to different characters who don't have much to do with the story. I've seen this before in other movies where it shows a different perspective. Not the case here.
Also, whatever is happening on screen that is actually tolerable quickly ends. For example, there a few scenes with a slight instrumental score that builds up and...then it just cuts to another scene. I'm aware that this can be a dramatic effect. That's definitely not the intention here. It's just bad editing.
Finally, there's the "ghost" who just screams in a way that's not scary or unintentionally funny. It's annoying and it happens a lot throughout the movie.
All of the scares have been done before in better ways so you can see them all coming. Then after one of them, the movie is over. At that point, a wave of confusion swept over the audience as I could sense we all felt that we had wasted our time. Someone did a mock clap and laughter ensued. It was better than the whole film. Simply put, AVOID.