I was watching this unlisted video on the making of the GMK Godzilla suit and some things popped out to me - https://www.youtube.com/watch?v=0zF_-7l4qvI
I know they tried making the suit as self-contained as possible, with an animatronic face allowing great expressions, but I was unaware of other features in the suit - like the breathing chest and moveable fins (an idea I like a lot). I don't know if they show up in the movie but they were a surprise to me. You can see these at the tail end off the video.
Another thing is that it's a common bit of trivia that they tried making Godzilla lean over like a T. rex or G98, but I've never seen much evidence to support that - If anything if looks like the maquettes and in progress suit is even more
upright with much better posture than he has in the final film, where they had to compromise with the slight hunch giving him his infamous pot belly.