I just recently re-watched this film (Japanese version with English subtitles). I thought it was pretty good. The movie did a good job creating a scary atmosphere when Godzilla was attacking Osaka. The black and white helped out a lot in this respect. The fight between Godzilla and Anguirus was well done and very animalistic, keeping with the tone of the movie. I felt that Kobayashi was a very likeable character. In fact, it was somewhat refreshing to see a film with "regular" people (the fishery owner and his workers) as the main stars instead of military officers and scientists as are typical of monster films. It gave you some glimpse of how regular people dealt with the aftermath of a monster attack. Masaru Sato's music was also fitting, although one does miss Akira Ifukube's signature scores.
On the downside, the movie is not terribly exciting. The movie can be boring in spots. I also felt that Kobayashi's fate could have been handled differently.
It is pretty clear that Toho had done all that they could with the heavy, serious Godzilla. That is why the next movie, King Kong v. Godzilla,
was such an important change of tone. Still, I think GRA was a good attempt to try to recapture the feeling of the first movie while making if different enough to warrant a viewing.