Part of this may be "super hero movie fatigue." There is a sameness to most of these films, even the good ones. It is hard to describe but it is something everyone (who isn't a complete fanboy or fangirl) senses after repeated superhero exposure. Iron Man III is good. The Avengers was a lot better than such an ensemble film should have been (a LOT better). But there is also something anticlimactic in all of them.
Maybe it is because we know none of the main characters are ever in any real danger. There has to be a part 2, part 3 or part 4!. The comics kill off their characters with frequency (and of course bring them back with equal frequency) but at least that allows for some suspense.
But back to Man of Steel.
What are the best things about the film? Henry Cavill and Michael Shannon are both excellent as hero and villain. Cavill and company are probably the best group of actors ever brought together for any superman movie. Yes, I know, Christopher Reeves had a horrible accident and was a totally brave and admirable man. But Cavill is a better actor. There is an almost "Wolverine" side to this movie where Superman tries to hide and blend in. Cavill is good in these, all too brief scenes.
Shannon, the depth of whose character is regrettably only hinted at, is even better. The hints of the complexity of his character come from the notion that, on Krypton, everyone is genetically engineered for a duty--Shannon's Zod is the warrior-protector of the society. There could have been much more made of his conflict as a formerly "good man" but it is sort of left on the table.
This is an example of what is wrong with the movie; there is a great deal hinted at that is never fully explored. They cram a lot into the movie and they do it pretty well. This is never really boring (even if it starts a little slow). It just never rises to the level of, let's say, the Batman movies or the first two X-Men movies.
This said? With all the introductions out of the way? The way is clear for a more complex and higher end super hero film with Superman II. Let's just hope the fight scenes are a little less Transformers-like in number 2.
Some of the actors not mentioned:Diane Lane and Amy Adams also turn in decent performances. Lane playing Martha Kent does give her character depth in this film. She is a fine actress. And while Adams isn't given much to do here, she adds something to Lois Lane. This Lois Lane can do things for herself.
Once again, hope for future Superman movies. Filmmakers need to remember that audiences do not mind movies where there is talking--provided what is being said is interesting. Explosions are cool but so is exposition.