well considering the fact that JJ Abrams said he wanted a monster that has never been seen before and Neville page said he felt like he had accomplished that, i dont think its a ripoff of the Toho creation of Gojira. the producers did a good job of misdirecting the public with japenese themed names and ads. Even calling the working title of the movie "slusho" which abrams has depicted in other films as a japanese drink
http://www.slusho.jp/ .
Dont want to ruin anything for you, but if your going to see the movie just to find out what the monster is, pick another movie.
If you want to compare the monster to a previous movie, go see "the beast from 20,000 leagues"
if your still not feeling smart enough, google "1987-2004 ace"
then connect the dots to Ethan Haas (if there are any)
here's fun one, a site owned by JJ abrams to drop hints
http://www.1-18-08.com
well, i hope i brought the smart meter up some with my post.