'Man of Steel' is superior to 'Superman'
The film retells Superman's origin story -- only he doesn't call himself "Superman," which is refreshing because only an arrogant ass would call himself something like Superman. The film explains the emblem in a similar fashion to the 1978 film by showing the insignia as a sign of the House of El (which, incidentally, the new film reveals, is a symbol that stands for hope).
The studio and filmmakers probably don't understand the criticism either since the film is performing well at the box office, too, and seems to have singlehandedly reversed the moribund decline of the franchise.
There are two main types of critics of the films: those who know (or think they know) the comic book character so well that they can state that the film is a violation of the entire 75 year history of said character; and those who love the 1978 film (and usually the sequel) so much that they think anything that varies from it is sacrilege.
As everyone is aware by now, the film ends with Clark Kent/Kal-El killing the villain, which is so against Superman's code that he should have been reduced to a drooling idiot if he had to do it. Since by the next scene, which takes place in a non-specified but obviously much later time, he shows no sign of this conflict having affected him, obviously the filmmakers seem to imply he got over it too easily and too well.
One could argue that under the circumstances -- the Phantom Zone was closed, Zod could not be confined easily (if at all) and he was determined to kill everyone on Earth in revenge for Clark Kent/Kal-El stopping his plan to bring Krypton back to life, and was in fact about to kill a bunch of people right then and there, and Clark Kent/Kal-El had no choice but to kill him -- but that would ignore that the circumstances were created by the filmmakers. They could have had Jor-El provide Clark with a working Phantom Zone projector, or have Zod commit suicide because his life purpose was over. He could have had Clark somehow re-create Krypton in miniature in the bottle city of Kandor (which longtime readers will remember as a city from Krypton that was saved because it was shrunk and stolen by Brainiac before the planet's destruction).
So, OK, Clark didn't have to kill Zod unless the filmmakers wanted to have him do so. That's the choice they made. How does it work in the film? It was a hard decision for Clark Kent/Kal-El to make, but unless you don't believe in capital punishment, or defending yourself or your loved ones with lethal force in cases of home invasion or war, then get over yourself and suck it up. You would have done the same thing. "Yes, but I'm not Superman," you reply. Well, guess what: Clark Kent/Kal-El isn't Superman either, and it's a good thing, too.
Sometimes Man of Steel critics state -- other times they merely imply -- that the first two Superman films are the ideal towards which all other Superman films should aspire. Really? Did they see the same films I did? I like them, at least in parts, but they contain many of the same problems, plus more besides.
Wanton destruction of property? Both earlier films have that in spades.
Superman killing someone? Try three people, the three Krypton villains art the end of the film after they have been depowered. (OK, it doesn't show them being killed, but we never see or hear of them being imprisoned or rescued from wherever they slide in the Fortress of Solitude. The comic book bit where the hero doesn't actually kill the villain, but allows them to die in an accident always seemed pretty wimpy to me. He's not a killer because of a technicality. I think that's still manslaughter.) Anyway, they weren't even much of a threat to Earth. After they take over, they mainly sit around the White House acting like the cast of Marty ("Whadya wanna do?" "I dunno, whadya wanna do?"). At least Man of Steel gives them some sense of purpose, some reason for behaving the way they do.
Face it, Christopher Reeve's Superman is a self-aggrandizing showoff, an arrogant glory hound who puts on a costume before he's ever shown using his powers to help other people. Only an egotist would call himself Superman in the first place.
Also, he's a bully who goes to pick a fight with someone who roughed him up when he didn't have his super powers after he gets his powers back. And, as another commentator has pointed out, Superman chose to give up his powers in the first place because he was horny.
(For the record, Richard Donner's director's cut of Superman II doesn't contain many of the flaws of the Richard Lester version originally released, and is a far better film.)
Out of kindness, I won't go into detail about Superman III, Superman IV or Superman Returns, which I'm sure no one wishes to defend.
If you're a fan of the comic book version(s), he's little better. For most of his run, he lives a double life, attempting to romance an uninterested Lois Lane while posing as a clumsy, socially inept dork, while pushing her away as a nuisance when he's being himself. (Unlike with true love, he wants Lois to love him not for who he is, but for who he's pretending to be.)
Also, for most of those years, he didn't need to even think about killing anyone because even his worst foes weren't trying to kill anyone, except maybe kill Superman himself. They were either trying to pull overly complicated robberies in Metropolis (why, if you're a crook, do you decide to rob banks or museums in the one city in the world that has a resident godlike man defending it?) and/or to defeat Superman as if it were just some sort of game.
Frankly, there's really no good reason for someone to dress up in a flashy costume to get cats out of a tree. There isn't much reason to do so to catch bank robbers either. About the only reason to do so is because you're fighting guys who are also dressing up like that, or to let people know that someone very important is coming and to act accordingly ("Kneel before Zod."). If you're humble and not seeking glory, you don't dress like that. If you're meant to be a symbol, you don't show your face either. A mask is de rigeur.
Then there's the whole schizo Clark Kent-Lois Lane-Superman triangle. Is that truly a sane way to behave? Only if you have no feelings for Lois and just want to maintain your secret identity. In any sequels to Man of Steel, it looks like Lois and Clark will have a more honest relationship.
There are many versions of Superman out there. He was not conceived of, developed and written by one person with one vision. And each writer's vision has been influenced by the times in which they lived (one version had a mullet).
I'm thankful for Man of Steel for several reasons: there is no sign of Kryptonite, which is a mostly lame plot device; Lois Lane behaves like a more-than-competent reporter (and appears to be of an age where that is believable) rather than a bad screwball comedy heroine; and while there is a brief glimpse of the Lexcorp label, there are no hare-brained real estate schemes involving the murders of millions of people. All those elements were also present in the 1978 film, so revered by critics of the new film. Do they wish they were present in the new film?
I've also seen several critics say the sequence on Krypton was too long. I liked it myself, but I'm more of a science fiction fan in general than a Superman fan in particular.
I didn't care for all of the fight sequences -- I didn't care for them in Superman II either -- but they may have been some viewer's favorite scenes.
I also didn't like the learning-to-fly scene. It looked silly, like he was jet-powered. I always saw Superman's flying as more of an antigravity thing, that he could just sort of float there, though he could go faster than the sound barrier if he chose to or needed to. Man of Steel seemed to imply in that first flying scene that he couldn't fly unless he went very fast. (If you want Superman to get back to his roots, flight is the first ability that needs to go. He couldn't do it until the comic book makers saw how silly he looked jumping in the original Fleischer Studios animated shorts.)
Yes, in most cases Superman wouldn't need or want to kill anyone, but -- as I read in a book on writing -- a book or a film is about the most significant or most important or most unusual event in someone's life. That's why most series peter out. Either they become absurd because they try to make each successive event bigger than the last, or people start wondering why these less significant events warrant a book (or film). Man of Steel isn't about a random, pedestrian day in the life of Clark Kent/Kal-El, but about big issues, difficult decisions. You can argue that he made the wrong one, but that shouldn't in and of itself make the film a bad one. So if you don't like the film, ask yourself why, then ask yourself if the problem is within the movie or within yourself.