Disclaimer: This article only focuses on GTA IV and not on the 2 expansions.
When you take a look at main stream games these days the easiest and most tempting approach to creating a main protagonist for your game will be your average "grim & gritty" "war is hell but at the same time I love chainsawing shit to death" grizzled (white) male with short to no brown hair.
Also known as the Gears of God of Splinter Cell hero.
In case creating a superficial and stereotypical cop out story becomes to hard to do just stick to your average "wise cracking sociopath dipshit without any clear motivation for his actions".
Also known as Nathan Drake.
The idea behind cardboards like Nathan Drake is simple and almost logical.
When I play a game like Splinter Cell where I really really really love taking out dudes and looking cool doing so I do it for that reason alone; I want to rip out some spines and have fun.
I don't do it to avenge the daughter I as a player never cared about to begin with.
Which (fina-fucking-ly) brings me to the Grand Theft Auto IV.
GTA IV was in terms of gameplay total let down, which can be summed up in a single sentense:
It had nothing to do and the stuff you could do got boring as fuck.
But where the game truly shined was in the character department, in particular Niko and his cousin Roman.
Unlike Cardboard Drake, Roman is a believable flawed character.
A guy who believes in the american dream, comes to the states and builds a small business as a taxi driver showing off his passion and struggle to rely on himself.
But on the same time he gambles away his money and gives in to the flaws of temptation.
However he remains sympathetic because he is still trying to build a better life and to afford taking care of and marrying Malorie.
Roman certainly doesn't show the complexity of James Sunderland from Silent Hill 2 or Wander from Shadow of the Colossus regarding his personality and actions.
But similar to somebody like the Prince of Persia (in The Sands of Time) or Travis Touchdown he shows flaws and makes mistakes while still keeping integrity and his hopes and thoughs and beliefs straight.
While Roman appears like a usual flawed human being Niko makes for some fun tragedy and bitching about human condition.
Past GTA games either realized that the main character had to be a psychotic murdering lunatic mostly influenced by Mr.Blond from Reservoir Dogs (read: Tommy Vercetti) or failed to realize that and had him endorcing in romantic relationships, taking care of his crackhead mother and giving money to his deadbeat brother (read: Victor Vance) without acknowledging that the player would then skip that shit to drive a tank up a hooker's ass.
Niko actually manages to succed in this insane balance act between being a psychotic killer and taking care of his loved ones.
In this scene I for the first time really got what made Niko tick and why GTA IV tried to be so anoying with the friends calling you to go bowling.
Niko was mentally scared by the things he witnessed during the war that he is no afraid of nothing, not even his own actions. The first time you kill somebody in GTA IV Niko actually says "I actually wanted to kill nobody in this country" without trying to come of wise-cracking.
Up to that point in the game the horror's he endured were only hinted at and now you actually realize that Niko hates nothing more than killing people even though he is that good at doing it and now you understand that this veteran would rather spend time just doing what the empowerment fantasy dipshit in us hated about GTA IV, driving friends around and playing bowling with them, enjoying fast food, going to a strip club etc.
However when you as a player decide to go postal and butcher half the people in Liberty City you can blame it on Niko's almost destroyed psyche.
Most of the "do you want this dude to live or die" choices in the game were totally useless and superficial except for Niko's final encounter with Darko Brevic, the man responsible for most of the shit Niko faced during the war.
This scene and the final outcome does not determine anything regarding the endings of the game.
Instead it shows how Niko either gave in to the easy temptation of revenge by killing Darko or how he finally managed to use rational deal with his troubled passed by starting a better life (mostly) free from death and sorrow.
It's these kind of choices that really call for player agency where you get to witness a character's development and then take part in shaping what kind of a character they are in the end.
That way this choice between doing what would be right - but hard to do and what would be wrong - but very very easy to do applies for both Niko and the player and respectively reveals what kind of person you are.
So yeah, in terms of believable human character development and moral ambigouity and psychological complexity GTA IV is paired together with the game's satire and delusion of the american dream probably the best GTA game, which is why I can not wait to see what the fuck will happen with the story of Red Dead Redemption.
Even though the gameplay was fucking boring until Ballad of Gay Tony came out.