YEAH WELL IM NOT THE BEST WRITER, BUT PLEASE... BE GENTLE!;)
Story:
I would begin the movie with destruction of Krypton, like they did in Birthright and then, (while the begin credits goes) i would show how Clark came in earth and what kind of childhood he had and after the credits, i would make the movie jump years forward and put Clark in Africa as the travelling Journalist. When something horrible happens in there he returns to Smallville to see Kents and think about the direction of his life. In their, inspired by Kents he creates the identity of Superman.
He travels to Metropolis and gets the job from Daily Planet and is introduced to Lois Lane. With her, he starts to investigate major arms dealing in the city. Someone deals new powerful weapons in the streets. And while following the clues Clark/Superman and Lois crosses paths with criminal organisation Intergang and its boss Bruno Mannheim.
However Mannheim turns out to be just the dealer and the real mastermind behind him turns out to be Lex Luthor. One of the most richest men in Metropolis and also a major weapon manufacturer. HIS PLAN: To make Metropolis a one hell of a place to live and then come out as its savior. MOTIVE: Power and glory.
When Clark/Superman makes more damage to his plans, Lex hires Mercenary John Corben to deal with him. Corben sets a trap for Superman and they fight. Corben of course with the big battlesuit, which he had "stealed" from LexCorp.
The suit explodes or something in some situation and Corben is wounded badly.
While Superman and Lois starts to get more romantically involved with each others. Lex transfers badly wounded and vegetable Corben to his laboratory and promises him the revenge, if he volunteers to Luthor´s experiment to create a super soldier. Corben agrees and Metallo is born!
However Corben´s now unstable mind falls apart and he totally looses his identity. Only thing he wants now is to destroy everything. He steals a terrible experimental bomb from LexCorp, which could wipe out whole Metropolis
Superman has to face this terrible threat, which powers match his own and save Metropolis from totals destruction. Superman and Metallo has serious and bloody fight and whole Metropolis (which people has first been doubtful about Superman´s motives) follows these horrible events. Finally after big fight Metallo is destroyed and Superman who has evidence about Luthor´s involvement, goes to arrest him. But Lex is awaiting him with his own powersuit and they get in fight which ends to Lex´s loss. Lex goes to prison.
In the epilogue, there happens something that sets the things for sequel.
(For example Luthor could have get the weapon and Metallo blueprints from Brainiac or something)
CAST:
(I think it speaks for its own)
HENRY CAVILL (Clark Kent / Superman)
AMY ADAMS (Lois Lane)
MICHAEL FASSBENDER (Lex Luthor)
TIMOTHY OLYPHANT (John Corben / Metallo)
KEVIN COSTNER & DIANE LANE (Jonathan Kent & Martha Kent)
ED HARRIS or RICHARD JENKINS (Perry White)
PAUL DANO (Jimmy Olsen)
MILLA JOVOVICH (Mercy Graves)
With
JOSH BROLIN (Bruno “Ugly” Mannheim)
And
JAMES CAVIEZEL & CHARLIZE THERON (Jor-El & Lara Lor-Van)