The original Japanese version did make appearances in art-houses in 1982 and 2003. The first time I saw Godzilla, King of the Monsters was on TV on TBS back in the late 1980s. The first time I saw it on film it was in 2004 and it was the subtitled Japanese version. The American version had been released many times on VHS and twice on DVD without the Japanese version. These DVD versions (Scimitar, 1998; Classic Media, 2002) have long been considered inferior. All you ever probably ever need to know about them can be found here : http://www.tohokingdom.com/dvds.htm
I. Gojira / Godzilla (Classic Media)
Released on September 5, 2006. Two DVDs.
This was the first time the Japanese original was released in North America. I own the DVD release. DVD1 has Godzilla (labeled Gojira), DVD2 features Godzilla, King of the Monsters! (labeled Godzilla). Aspect Ratio is 1.33:1. Out of Print in single release shown above, but available as part of The Godzilla Collection (2012) with the other good Classic Media Godzilla DVD releases. The DVDs, sans booklet, are available in a new reissue with a new cover :
Special Features :
Making of Godzilla Suit Featurette
Godzilla Story Development Featurette
Audio Commentary by Steve Ryfle & Ed Godziszewski
Trailers for Godzilla & Godzilla, King of the Monsters (DVD1 & DVD2, respectively)
"Godzilla's Footprint" by Steve Ryfle (Booklet discussing Making of the Film)
The Blu-ray release uses an unnatural 1.47:1 picture frame, as the film was shot in the Academy Ratio of 1.37:1. Only the Japanese original was included. The Special Features from DVD1 are included (in Standard Definition), but the Booklet is not. The Blu-ray is single layered. The main feature uses a 1080i resolution.
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II. Godzilla (Criterion Collection)
Released on January 24, 2012. Two DVDs or One Blu-ray disc (separate packages).
This is the only other authorized release of the Japanese original in North America. I own the Blu-ray (as do most other people who buy Criterion releases these days). Both the DVD and Blu-ray offer Godzilla and Godzilla, King of the Monsters!. The DVD presumably offers Godzilla on DVD1 and Godzilla, King of the Monsters! on DVD2. The Blu-ray is dual-layered and both films are presented in 1080p.
Special Features (virtually all in 1080i):
Interview with Akira Takarada (Ogata)
Interview with Haruo Nakajima (Godzilla)
Interview with Yoshio Irie & Eizo Kaimai (Special Effects Technicians)
Interview with Akira Ifukube (Composer)
Special Effects Photographic Featurette
Interview with Japanese Film Critic Tadao Sato
"The Unluckiest Dragon" - Audio Essay about the Fukuryu Maru incident
Audio Commentary of David Kalat on Both Godzilla and Godzilla, King of the Monsters!
Trailers for Godzilla & Godzilla, King of the Monsters
"Poetry After the A-Bomb" by J. Hoberman (Booklet discussing History behind Film and Themes)
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Godzilla (The Criterion Collection) [Blu-ray]
Godzilla (The Criterion Collection)
There is no real comparison. The Criterion Blu-ray shows a sharper image and shows far more detail than anything from Classic Media. Both use a mono soundtrack, so there is no "tampering" with the soundtrack. The soundtrack on the Criterion has been praised as bringing out the elements which have been buried under a layer of hiss and muffled sound. Classic Media's releases are interlaced, which is easily noticeable when watching the movie on a computer monitor. Criterion is not.
Here are screenshots from Classic Media's release : http://www.blu-ray.com/movies/Gojira-Blu-ray/5496/ and Criterion's release : http://www.blu-ray.com/movies/Godzilla-Blu-ray/31499/#Screenshots. The Classic Media's image is stretched out, lacks detail and suffers from an overuse of DNR. Criterion's image is sharp, but a tad dark in Godzilla's scenes. I would adjust the brightness and contrast a little if you wanted to make out more detail for those scenes. The clarity of image and sound is a noticeable improvement from Classic Media's DVD.
The Criterion includes the Transworld logo on Godzilla, King of the Monsters, which has not been seen on an official DVD release since the Scimitar disc in 1998. Classic Media does not, and while the audio is there, the image where the logo would be is black. Apparently Classic Media added three digital transitions in Godzilla, see here : http://www.dvdbeaver.com/film/dvdreviews20/godzilla_dvd_review.htm
The subtitles on Classic Media are yellow and on Criterion they are white. Note that Classic Media defaults to the subtitles being on, the Criterion default is off. Criterion translates more of the opening credits than Classic Media. Classic Media fails to give the credit for Akira Takarada! However, neither provides a full credit translation. There are forty-eight lines in the credit scroll with Kanji characters, each naming a different person. Translating or transliterating the lesser-known names who worked on or acted in this film may not give accurate results, especially in comparison to some other variation of that person's name elsewhere in literature. The Criterion booklet seems to give credits for all the production crew and almost all the cast, including all the major players. (Toho's crediting policy apparently was to provide a credit for just about anyone with a speaking role at the time). The translations are different.
Classic Media had a very striking packaging for its time. The image of Godzilla rising out of the sea, with the blood-red lettering, is instantly eye-catching. Someone had the bright idea to use a picture of the real full-body suit, not a publicity shot with one of the inferior clay models. The title would have been better as "Godzilla" in the large lettering and "Gojira" in small caps. The backing is very sturdy, it feels like the cover of a hardcover book. The sleeve is a little annoying. However, this fits extremely well with Classic Media's later Godzilla releases.
Criterion uses a thinner cardboard material, and has a sleeve that encloses all but one side of the Blu-ray tri-fold. When you open up the tri-fold, Godzilla's head pops out the top. The artwork is original, but the pop-up seems a combination of the Heisei and Millenium era Godzillas, and the art on the exterior of the tri-fold seems taken from Godzilla, Mothra, King Ghidorah, Giant Monsters All-Out Attack (a stupid title if ever there was one). The booklet takes adapts some publicity stills.
Unless price is the sole factor that will determine your purchase (Criterions always sell at a premium, but currently as of June 8, 2014 the price is very reasonable), both discs have unique features. The features may be a little sparser on the Classic Media, but that company was testing the waters with the first quality production of Godzilla. Moreover, features were planned to span the entire library to which Classic Media had rights. Moreover, they did not want to pay Toho for the rights to use the special features on Toho's Region 2 DVD releases. Criterion came up with different special features, as with maybe one exception (Akira Ifukube's interview), Toho's special features on its Godzilla DVD/Blu-ray are not to be found in the Criterion disc.
Both discs provide commentary for Godzilla and Godzilla, King of the Monsters. David Kalat had previously provided commentary for Classic Media's release of Ghidorah, The Three-Headed Monster. Kalat wrote "A Critical History and Filmography of Toho's Godzilla series" which has had two editions. The price dissuaded me from buying it when it was in print, and now it is Out of Print. Ryfle wrote "Japan's Favorite Mon-Star: The Unauthorized Biography of "The Big G". I own this book and it is a a reasonably comprehensive look at Godzilla's history until the end of the Heisei era; its now Out of Print. Godziszewski wrote "The Illustrated History of Godzilla", a book that has long been Out of Print (observing a common theme with serious Godzilla books here?) Ryfle and Godziszewski provided commentary for other Classic Media Godzilla DVDs. The commentary for the original Japanese Godzilla can also be found on BFI's Region 2 Godzilla DVD. The Classic Media DVD is very useful for people who do not own Ryfle's book, and I would assume the same could be said for Criterion and Kalat's book.
Both commentaries cover much of the same ground. Ryfle includes audio interviews from people like Terry Morse Jr., son of the director for the American footage of Godzilla, King of the Monsters! and others instrumental in bring Godzilla to the U.S. Kalat discusses certain cultural issues surrounding the film. I would recommend starting with Ryfle's commentary, then proceeding with Kalat's since the former is more geared to the kaiju novice.