Superman Returns was not "practically perfect." It was practically watchable. At points. Which is a shame, this could've been the capstone to a series of spectacular comic book movies that proved the stereotypically kid-oriented picture books packed the complexity and pathos needed to transform a popcorn flick into an epic. The first two X-Men fit the bill, and Batman Begins was among the best movies I've recently seen. No defense, of course, is needed of the Spidey's two flicks. X-Men 3 and Daredevil, while not quite up to the level of the others, were misfires that nevertheless exhibited seeds of greatness. Superman Returns did not.
To be fair, Superman is the toughest character of the set. As the comic book industry matured away from its characters' invincibility and towards their vulnerability, Superman was always the toughest of the bunch. In the old comics and cartoons, they used to just invent new powers by the episode, everything from ice breath to turning back time by reversing the earth's rotation. It was a bit silly. But, at the time, popular. Superman's strength, however, gave way to Wolverine's rages, Spiderman's conscience, Xavier's vision, and Batman's darkness. Comic book characters began fighting themselves, their enemies little more than triggers for their internal conflicts. Superman, lacking these troubles, was left behind.
So the comics had to find ways to subvert his invulnerability. They didn't, generally, do this through strategic usage of kryptonite. Instead, they pitted Superman against his need for public legitimacy (as in when Luthor became president) or his desire to simultaneously have and not endanger loved ones. The movie, however, takes neither of these approaches. Luthor has no public legitimacy, he's a crook with a coterie of morons providing comic relief. His plan appears entirely taken from those crystal growing chemistry kits I had as a kid -- he's going to use the krypton crystal's unexplained ability to sprout in water to create a new continent on which folks will then pay him to live. Oh -- and this continent will fall atop North America killing a bajillion people.
The plan, of course, makes no sense, all the more so because Lex is already rich. His initial motivations (which are actually interesting), hinted when he condemns Superman for keeping his powers to himself and not spreading divinity across the population, totally dissipate into mundane evil geniusdom. He's not humanity's mistaken champion, protecting them from a force beyond their control. He's just an odd dude with a vendetta, a formulation that could scarcely be less interesting. As for Lois, she sorta-kinda moved on, is angry that he left for a couple of years, wrote a possibly interesting editorial about why the world doesn't need him, but is swept off her feet as soon as he returns. Some storyline. There's no tension or tough moral dilemmas for Superman -- he's got a girl he loves but who has some logistical problems, an enemy he's got to defeat, and a lot of responsibility. And that's the movie's flaw -- this is a Day With Superman, not the The Day With Superman. You get the feeling you're watching an average set of chores for the hero, not a particularly troublesome, tricky, or apocalyptic moment. And what's the point in that?