People seem to strangely forget that Supes is a really friken sad character. Honestly, the only thing that makes him better than Batman (imo) is that he hasn't been parodied to the point of oblivion of being overly whiny over Krypton (along with his entire people) getting nuked.
Not sure I buy this. Unlike Batman, who was old enough to understand what happened to his parents (he's usually between eight and 12 years old) and is often consumed with guilt and rage, Superman is almost always portrayed as an infant, sometimes a newborn, when Krypton is destroyed. Consequently, while I believe the character is sad about what happened, it's more... theoretical to him than it is personal. Superman was raised by loving parents in an environment that just screams "traditional" (read: idealized) Americana. There's little sad about the character in that respect.
What they're doing in these Man of Steel flicks is turning that expectation on its head. While I would argue that Kingdom Come (by Mark Waid and Alex Ross) offers a similar treatment, MoS (and apparently DoJ) seem to want to grapple with the concept of what makes a hero and the impact such struggles have not only over "normal" people, but over the character of Superman himself. There's a lot of sacrifice, angst, and reluctance in MoS's Superman. He's reluctant to take on the mantle because, like his adoptive father, he's not sure people can handle it. This causes him to experience some of the worst humanity has to offer (the bullying he endures throughout the film is really something to consider... Only once does he really lift a finger). Like KC's Superman, MoS is very much concerned about being a hero because he's not convinced that people really have an idea of what a hero is. In short, the MoS treatment of Hero is far more ambivalent than what we've been seeing in the Marvel Studios movies where that sort of struggle is much more muted, assuming it exists at all.
As for my preference, while I'm all for a more... conflicted stance regarding the Hero and like the idea of a Superman who is at the heart of that conflict, I think letting him go too dark not only diminishes him if not done properly, it also diminishes Batman's status in that regard. The additional possibility that Batman
further diminishes the character IMO. I'm all for grimdark. I like grimdark, but only when it's appropriate for the characters(s). I'm not yet sure if they've gone too far with Superman in this film (won't know until next year I guess), but I am concerned.