The problem with Superman is that if he is portrayed as too nice and 'perfect' then people will just walk away and go view something grittier and realistic, like Batman. If instead they portray the movie as more realistic and Superman being fallible and dark, then it's too much. He can't really win.

DC just isn't able to produce lighter films that retain a solid, emotional serious core. I agree with Shauna: the Marvels pull this off to great effect many a time. DC is attempting to be receptive to what they think audiences want. They looked at how well the Dark Knight trilogy with the gritty and dark batman did, and attempted to emulate that, but... I guess they overdid it.