For a summer movie built around giant robots punching things, though, Pacific Rim has surprising thematic depth. The main themes running through the film are family, unity, and coming together--witness the nature of the jaeger pilot teams, the manner in which the jaegers' mission is fulfilled, and the things that are necessary in order to do that. Behind those, though, there's a pretty strong environmental message--really, the kaiju are a pretty blunt metaphor for climate change.
Consider it: powerful forces erupt from out of sight, emerge onto land and devastate cities. The countries of the world cooperate at first and take active measures--the jaegers--to beat back the threat, but as the tide begins to turn, the sense of unified resolve splinters and the leaders choose instead to build giant walls to protect the land from the threat of the ocean; walls that may or may not be finished in time, and which may or may not actually protect the millions of ordinary people on the coasts immediately behind them, while the rich and powerful flee to "safe zones" inland. Remind you of any projections? The kaiju themselves are almost as forces of nature within the movie itself; consider that a powerful kaiju is a Category 4, the same way we categorize a devastating hurricane, and the opening narration explicitly draws that comparison ("in a jaeger, you can fight the hurricane").
That's why I have such a problem with part of the film's climax. If you've seen it, you may already know what I mean. If you haven't, wait until you've seen it to read the rest of this, unless you don't care about knowing what's to come.
Here's a good spoiler break--created by the Jaeger Designer.
So, it's the end of the movie, and Gipsy Danger and Striker Eureka are marching across the bottom of the ocean to deliver a nuclear weapon to the Breach, the dimensional portal through which the kaiju are invading Earth, and thereby seal it. Things go wrong, because of course they do, this is a movie for hell's sake. The weapon is unusable, and the hero pilot of Gipsy Danger must seal the Breach by self-destructing the jaeger's own nuclear reactor.
Oyyy. To put it simply: NUCLEAR REACTORS DO NOT WORK THAT WAY. You can't turn a nuclear reactor into a nuclear bomb any more than you can turn a 1989 Geo Metro into a fuel-air explosive.
This is a regrettably widespread misapprehension, because some goddamn writers don't make an effort to actually understand how things work--but, hey, I get you. You might be saying, "in a movie about giant robots punching giant monsters, you're getting angry over something like this?" Yes, I am. Things like kaiju and jaegers are impossible; you're not going to have 300-foot monsters in reality, and the idea of building 300-foot battle robots with modern technology is purely ridiculous. I can, however, suspend my disbelief on that point--jaegers and kaiju are the very core of the movie. Since they do not, and cannot, really exist I can forgive a lot of spectacle about their capabilities.
Nuclear reactors, however, do exist, and it is not very hard to treat them accurately. Pacific Rim is already asking a hell of a lot from me to suspend disbelief over jaegers, kaiju, a giant wall built around the entire Pacific Ocean... asking enough, really. It does not get a free pass on mischaracterizing something that actually exists.
There's more to it than that, though--a rather pernicious "more," the way I see it. It's the illusion-of-truth effect; people are more willing to believe something they've encountered before. Now, Pacific Rim isn't making any kind of statement here--the reason the whole "nuclear meltdown self-destruct" thing was used was because it's a simple kludge for the writer and it's direct. The problem, however, is that it generates another little data point fluttering around and waiting to attach to something. It's another piece of "something that I heard somewhere" that nuclear reactors explode.
The kicker is that the way I see it, this runs at cross-purposes with Pacific Rim's environmental themes. What was true in the 1970s is true in the 2010s; when it comes to electrical generation, for most of the world there are only three choices: nuclear, natural gas, or coal. Not everyone has geothermal vents of dammable waterfalls, after all, and while renewables are admirable targets to shoot for, they're still far away from being able to support the brunt of demand themselves. While natural gas has a comparatively low CO2 emission rate, the fracking necessary to get it is causing earthquakes hither and yon, and the pollution from coal-burning plants kills hundreds of thousands worldwide every year when everything is working normally.
But you don't see Greenpeace standing in front of the bulldozers that the Germans are using to build those dozen new coal plants that are replacing all of its nuclear plants, because it doesn't fit with the common environmental ideology that nuclear is the worst of all things. No, you just see well-meaning movies that unintentionally shore up the foundation that makes that kind of ideology possible.
Nevertheless: Pacific Rim is fucking awesome. Go see it.