Everything X said, more or less. They did an amazing job with this movie. Everything about the Big G himself is flawless. Did you think the design didn't work? Too fat, teeth too small, eyes shaped wrong? Shut your whore mouth and wait until you see him MOVE before you say that. Stills and brief reveals do not do him justice in the slightest. You have to see him on screen, literally larger than life, moving and fighting to appreciate this design properly. Its... honestly, its how he always looked and moved in my head.
Now, X did the point by point so I'll go a little less deep. I've mentioned before, some of my favorite bits of Godzilla films are the body language he displays. A good suit actor (with a good team to move the tail and the facial animatronics when applicable) can make him a character who emotes as well as any other when they try. They did it just right in CG. The way he holds his head just before smashing the male Muto with his tail is EXACTLY the way I remember it from King Kong vs Godzilla ages ago. The way he stands before unleashing his huge "come on if ya think yer 'ard enough!" roar? It somehow conveys this blend of revulsion, anger, and hunger to fight. You can totally see him thinking, plotting out the best way to burn this or smash that. It is glorious. Just the way he walks is a show of raw confidence. The way he looks around when naval bombardments are hitting him in the face is a look of total apathy. There's a bit on the Golden Gate Bridge where we get this lovely closeup of him lightly gripping one of those huge damn cables what hold the thing up, lightly feeling it between his fingers. Not trying to tear it in half or break it. Its a simple exploratory thing, like a human running an errant string between their fingers in a "what's this now?" sort of way before he loses interest.
They also remembered one feature of the older movies that rarely gets featured these days: Godzilla is unaware of just how fragile things around him are. He clearly expected that building he smashed when he crushed the male Muto to take the hit and keep standing. It didn't, and it took him completely by surprise. It makes him seem clumsy, in a "doesn't know his own strength" kinda way.
Now, a slight quibble with what others have said. And this applies to folks in the audience as well as X and Reg. Godzilla doesn't come off as heroic. He doesn't come off as malicious either, mind you, but not heroic. A hero has to notice that he's saving someone. He has to be fighting a menace for the sake of others. Godzilla rarely if ever seems to notice the humans exist. He kills who knows how many just wading up the beach. He scraps multiple ships just standing up. He does take a couple missiles that would have killed a bunch of kids, but I for one don't believe he did it on purpose. He just happened to stand up at that moment. The only time he takes any direct notice of a human is Ford Brody, when G is on his hands and knees from the building falling on him. Its the only time he seems to see a human, and he doesn't really seem to care much.
Now, about the Mutos themselves. I love their design. It does not come off as a Clover ripoff the way many sites seemed to think. There ARE similarities, mostly in the limb configuration, but that's about it. They're very functional designs, with the bio-luminescence they flash in time with their EMP abilities giving them a sinister look. THEY do notice humans, and intentionally kill them. They seem to understand "this one killed my eggs" or "those little shits took my food." And the scene of the two meeting and bonding, complete with head nuzzles and the male making a gift of nuclear food to his new mate is an oddly sweet moment from two otherwise deadly creatures. X hit it on the head with this one, they're freakishly dangerous and have to be prevented from breeding for the sake of mankind, but they're just wild animals doing what they do. You can't hate them for it any more than you can hate Godzilla for the destruction in his wake.
One final bit, for now, I could say so much more here if it wasn't so late for us folks what have to wake up at 3AM tomorrow: Apparently loads of folks in my theater had never seen a Godzilla film before. When G is headed to the bridge, I seemed to be the only one (judging from whispered questions and such in the dark) who said to themself "He's not gonna go under you this time guys." I heard people asking aloud "The hell is happening now?" when Ford is suddenly lit by that bright blue glow from above. And then the spines start lighting up and I swear I almost got up and did the Snoopy Dance out of sheer joy. I saw it coming and it was still every bit as awesome as if it had been a complete surprise. Maybe even more so, because I know full well thanks to those whispered questions that I got to share some folks' (including a number of kids') first Godzilla experience. And that is more than a little awesome right there.
One final side-note (for real final this time for now): Godzilla, King of the Monsters, Savior of Our City? Yes... but not on purpose