Man of Steel was awful; for a large number of reasons. That post covered what was actively offensively bad about it, but to cover all bases we’d need to do as many comics as we do about the TASM films. And we’re not doing that. The TASM films might be bad, but at least they’re both interesting and entertaining. Man of Steel was simply more Zack Snyder excretion.
Zack Snyder loves martyrs. “You must sacrifice your values and/or everything that is important to you, in order to save others” is the theme of every one of his movies. No, literally. I’m not exaggerating. Superman was intentionally created as a messiah figure, but not as a Jesus figure – he was created by two Jewish men, for a start. This article explains it just as well as I could do here (although your mileage may vary on its other points). The idea of ‘Superman is Jesus’ certainly didn’t originate with Snyder, but it damn sure fits into his wheelhouse, and it reaches ridiculous new heights in Man of Steel.
Frank Miller… well, I don’t know what to say about Frank Miller that hasn’t been said before a large number of times. Critical opinion is pretty divided. I used to say I liked his earlier stuff, and that his work only got bad later, but now I’m not even sure of that. I think probably it was always bad and I just didn’t notice at first. It’s quite evident in the Batman side of things for Batman v Superman: Dawn of Justice, anyway. (I don’t even know where to begin making fun of that title. There’s too much material compressed into too tight of a space; incidentally, this is the same problem with how Frank Miller always draws Batman himself.)
The idea of these two glorified teenagers (everything must be DARK and GRIM; that’s how you make a film MATURE!) making filmic decisions a scant few feet away from the director of such a well-crafted film as Argo – and then giving him directions, even! – is just baffling.