As much as I LOVE grand 5.
It isn't very serious.
It's much more comedic than grand theft auto 4.

In fact.

Grand theft auto 4 is pretty "deep" game.

Niko is a war veteran.
And his whole life he was searching for the man whole betrayed and killed his war unit.

When he finally finds him, You have the choice of killing him or letting him live.

Either way.
Niko learns the same lesson.
"revenge salves nothing".

Killing Darko leaves Niko to realize.
It didn't salve anything.

And letting him live, is arguably better.
As Darko is "already dead".

It's hear Niko learns Roman was right all the times he told Niko about learning to forgive.

And if you choose to finally start forgiving people (by not killing Dimitri) it leads to the death of the very person who wanted you to do this.

Even if you kill Dimitri, it again leads to the death of the very person that told you to do this.

That's pretty deep man! :(