I'd argue otherwise. I think actual adults would take more to the original than they would Man Of Steel. It's a better told story with charm, wit and imagination. It has fully realized characters [agreed]. It has a real romance angle [that's one of it's strengths, and flaws]. It's mythic. [agreed, though I would argue that there's a mythological element to MOS]
Just because you're not a teenager anymore, it doesn't make you an adult. Eventually you reach a state of mind and a state of being where explosions don't matter and all you want is an engaging story [that sounds a tad pretentious. I personally found Clark's struggle to fit in and protect humanity to be engaging]. All the CGI spectacle in the world couldn't save Snyder's film for me. It was exhausting and tedious by that point. [I actually agree.] And don't even bring up young children. I'm certain that young children would take more to Donner's movie than Snyder's. Not even close. [Depends on the child.]
Superman The Movie will live on forever as a timeless classic. I just don't see time being as kind to Man Of Steel. [I like the film, and I agree. I think MOS will age better than some think, because of its attempt to combine the FX driven action with realism, character, and plot. But it's not a game-changer and is too controversial to have universal appeal.] It doesn't have those same qualities. It wasn't as good a film.[I think Superman:TM is more fleshed out than MOS, but MOS does a good job at capturing something that hasn't been shown in film for decades. The full effect of his power.]