I shall summarise: It's awesome. This probably contains spoilers. If you're not into having things spoiled, then, uh, stop reading. Or don't. Your choice.
Pacific Rim is one of those films that takes an utterly ridiculous premise and puts all its chips in, producing something completely enjoyable. The premise, such as it is, is that there are a bunch of gigantic electric dinosaurs emerging from a hole at the bottom of the ocean, and man has built a bunch of enormous robots to fight them with. Because nothing else worked. Because there can't possibly be a simpler solution than gigantic super-complex machines that mimic the human form. It's a bit like The Core in this regard, in that it takes something ludicrous and plays it for all it's got.
I think the entire film can be summed up in one scene from the trailer: The giant robot walks calmly out of the ocean into the streets of Hong Kong, dragging behind it an ocean liner, whilst the enemy dinosaur grins at it from the far end of the street. After raising the ship like a baseball bat, the robot then swings the boat at the dinosaur's face -- all of this occurs to the film's theme music (all six notes of it), and they properly chose to play it, for the only time in the movie*, on guitar. Proper, old school, heavy-ass guitar. This is robot violence porn at its finest.
Everything about the film is massive, awesome and fun. It goes boom, and it goes boom a lot. There're explosions, missiles, electricity, dinosaurs, alien entrails and whacky scientists. The heroes are appropriately heroic, and the villains are massive and hideous.
I thoroughly enjoyed the film.
I feel bad, but I can't help it. It's expected of me. I have a couple of nitpicks. They're not big deals, though.
Hollywood is currently drowning in Australian actors. Everyone who's ever appeared in Home and Away or Neighbours seems to currently be starring in a superhero franchise (except Alf Stewart, who should be). Somehow, the creators of Pacific Rim couldn't find any actual Australians to play their Australian characters, so they settled for an American and an Englishman, both of which proceed with the most embarrassingly atrocious attempts at the Australian accent I've heard in a long while. There's also an "Australian" newsreader and interviewee, both of which sound terrible. Surely it wouldn't have been too hard to cast a couple of Australians as the Australians.
I also found the two whacky scientists were a bit too whacky for my liking. A good comedy duo has an idiot and a straight man, but these two were both the idiot. Sorry.
Also, the bends apparently don't occur in the future.
* until the end credits, but y'know.