I don't understand the bit about having "been done before"... I hadn't seen a Superman story like that... besides, you're the one who is asking to bring back the Superman that has already been done...
As for "doesn't excuse the character for being sad all the time", well, two things:
1. He's not sad all the time. I know you love hyperbole, but you know that statement is not true. Both in MoS and BvS we see moments of happiness, determination and pride. If you choose to ignore that, it's your problem, not the movie's.
2. Being bullied as a kid, having horrifying experiences, having to hide your true self, losing your dad, discovering you're a freaking alien, feeling rejected despite trying to do good... I could go on, but you get the idea (or maybe not
). Of course that would be enough to make anybody feel pretty dejected most of the time. And again: he's not sad all the time
And, re: being "sad" after accepting his role in BvS, here it goes
again: in MoS he has found his place, he has accepted his role (with great cost to himself: your glib comment about breaking somebody's neck -how anybody fails to see the emotional cost it has on Superman is beyond me, but oh well) and sets out to be Superman. BvS shows us from the first moment, through Bruce Wayne, the conflicted reactions of people. It even states "Mankind is introduced to the Superman", and it is through a terrible, monstrous destruction. Even though Superman saved humanity, it was at a terrible cost, both to him and the unfortunate inhabitants of Metropolis. Here is the Superman, doing everything in his power to stop an engine of destruction that will wipe out humanity, but in doing so thousands die and he is forced to not just kill, but murder. So we have a world that suddenly has to contend with what amounts to a god -and an alien to boot- walking among us, and all hell breaks loose! He tries to do good, and people accuse him of murdering defenceless civilians, while on the other hand there is a masked vigilante terrorising a city and nobody cares.
And you're telling me it makes no sense that this guy gets pissed off or depressed every now and then?
Yet this is the same guy who flies off to save people in a burning building.
This is the same guy who walks into a hearing to be judged by people who distrust him, when he could just ignore them and keep doing what he can.
But to you this is a sad, mopey, loser who doesn't inspire and isn't an example of hope.