The problem with making a sequel to Man of Steel, in my opinion, is twofold.
One, the fact that it was directed by Zach Snyder to be a visual masterpiece and very little else makes it a really hard act to follow. Hell, I'm still confused as to how they're going to make a sequel to 300; I enjoyed the film, but I don't think I can handle any more men in leather underwear spinning around in slow motion. The thing that makes sequels possible, in my opinion, is a feeling that the world has not been explored enough, but when the first film is so focused on visuals, you don't get the kind of depth that you'd get from something like Star Wars, which looked good but also left its audience wondering about where their characters would go next, and what else the galaxy had to offer.
And that's the second thing, I don't think the characters have anywhere to go now. Krypton is destroyed, all the Kryptonians except Kal are dead, Lois already knows that Clark Kent is Superman, and everyone already agrees that Superman is a good guy. Superman himself has already gone through the Spider-man arc (gets cool powers, father figure dies, great power, great responsibility, kills someone and feels bad about it, gets the girl, etc.), and he's already broken Batman's one rule, so that arc is out. There's really nothing left for Superman to do, and there's really no one left to stand in his way. And, because of the previous problem, there needs to be something big going on in order for a sequel to be made about it.