I enjoyed the film, but I wasn't excited by it one bit.
Kate Bosworth was, plainly and simply, the wrong choice for Lois Lane. I think the character was written well - I like her conversation with her son about whether or not they're trespassing on Lex Luthor's yacht - but she simply failed to convey the strong personality and confidence that Margot Kidder and Teri Hatcher brought to the role. She came across as a little weak-willed, actually - unconvincingly arguing she and humanity don't need Superman, wheedling Richard White to convince Perry to let her pick her own stories to cover - and that's very disappointing.
Plus, on a personal note, I think she's also pretty unattractive. Neither pretty nor sexy. I'd rather see Lois played by a handsome woman like Margot Kidder, who was no bombshell but at least seemed like a woman. Teri Hatcher at the beginning of Lois and Clark was both beautiful and curvacious, as well as determined. Bosworth was . . . nothing.
I didn't much like Lex's scheme, aesthetically, but I'm prepared to say that it makes sense for the character as established by previous film continuity. His plans don't always make sense but I think he's always been looking to dramatically leap into a position of power, after which he can just use his new resources to batter his way through any problems or opposition that arise.
Kevin Spacey's performance was good, if restricted to a limited range by the script. It's a little jarring to hear folksy turns of phrase that would have sounded natural in Gene Hackman's somewhat hucksterish Lex's mouth coming from a more refined and aristocratic version of the character. Spacey didn't quite deliver lines like "This is kind of a little reunion, isn't it? Heck, I'm a fan!" either like he was mocking that way of talking or like he genuinely talked that way.
I thought that Richard White and "Jason-El" were very solid. I approve heartily of the child character contributing to the story without unreasonably overshadowing the main adult characters, and that he entirely lacked the attitude that passes for charming in badly-written kid roles. Meanwhile, I liked that Richard was a decent, even heroic guy who didn't even get overly jealous about Lois' involvement with Superman - and it's a nice touch that he doesn't take Clark Kent seriously as a romantic rival and get jealous about him, because it demonstrates that his worries about Superman are based in the awesomeness of Superman, not the maleness of other people Lois spends time with.
Frank Langella and Sam Huntington pulled their supporting roles off well, though I thought characterising Jimmy Olsen like he'd just stepped in off the street where he wore a flatcap and knickerbockers and sold newspapers to 1930s Chicagoans was a little awkward. That impression passed quickly once he had more to do than exclaim over Clark Kent and exposit the five years of Lois Lane's life that Clark missed. Langella was solid as Perry White, though given a little too little to do.
Finally, there's nothing I can really say to criticise Brandon Routh's performance. I thought it was interesting that they eschewed the massive Alex Ross look in favour of a "regular guy in good shape"-type Superman, which is obviously an element held over from the Donner films but which makes a lot of sense in terms of Clark Kent coming across as a handome and fit guy who doesn't stand out much at all. A huge, handsome, hypermuscular Clark Kent who's not on Lois Lane's radar requires a different characterisation where he's dismissed as a rural farmboy (as in Smallville, from time to time) or jock type. That's not the Donner mold, though, so it's not the way Singer plays it.
Like Christopher Reeve and, in fact, Dean Cain, Routh's Superman is the strong, silent type who looks resolute and disapproving when dealing with criminals. Admittedly, there's not a lot for Superman to actually say - and cracking wise like Spiderman or mouthing off like Wolverine wouldn't really suit the character at all - but it's interesting that Superman doesn't communicate much even with the people he's come to save (like the cops or security guards, whichever they were, on the roof with the crook and the minigun). Whether that evinces reserve on Superman's part and implies that he feels it's pretty obvious why he's there and what he's going to do, or simply a focus on doing the job without wasting time on reassurances until everyone is really safe, I don't know, but it's an interesting element of characterisation that's not always present in other versions of the character. Does it emphasise the ambiguities of Superman as an alien and a saviour that people don't always even know that they're being rescued by him until they're already safe?
My major criticisms of the film are in the pacing. It's simply takes too long to cover the events of the narrative. I'm forgiving of lengthy openings like the scenes at the Kent farm, especially in a film like this where the time it takes Clark to get back to Metropolis reflects the uneasy transition back into society he faces as Clark Kent and as Superman, but the rest of the film is packed with scenes which are just longer than they need to be: the first test of the Kryptonian crystal growth in the widow's mansion, every scene where electrical devices black out after the first few shots, and innumerable dialogue-free transitions and shots held at the beginning and end of scenes for what seems to be no reason.
Even some of the action sequences drag on longer than they strictly need to - Lois, Richard, and Jason trapped in the galley of the sinking yacht, for instance. Since there can be no question that Superman will save them, there is no real suspense, and there's even less the longer you draw it out.
The worst offender, pacing-wise, is the sequence after Superman pushes the crystal island into space and falls to Earth. I can deal with the heavy-handed Christ metaphor, and I liked the touch of Martha Kent in the crowd outside the hospital. Lois' whispering the truth of Jason's parentage (one presumes) into Superman's ear is likewise worthwhile, even necessary. Again, though, so much of it is tension-free - no-one in any theater above the age of five believed Superman wouldn't survive, and most of those under five would have known he would too, so why drag out this bogus medical revival so long?
I like the spaceplane rescue, and I like Superman saving the residents of Metropolis from the effects of the earthquake. I thought the special effects were flawless and very cool - kudos to the team for taking the new Smallville-style heat vision effects on board but referring to the 70s-style "beams of colour" version at the climax.
I agree with everyone who said that they're interested to see the next film, both because I believe Singer will learn from his misjudgements on this one (though I fear nothing can be done about Bosworth as Lois Lane) and because I'm curious to see how they play with the addition of "Jason-El" to everyone's lives.
I just can't say I got excited during Superman Returns, and I think that's a shame.