Lets really LOOK AT who Roman is, for a sec.
He's all excited to get Niko over to the US, and gives him a load of lies about the American dream. You feel like this is probably what people told Roman before he got there, and he's using the same trick. I bet a lot of people in real life emigrate from Europe to the US looking for the land of the free. Right from the start, that's pretty interesting.
He talks a lot about starting the cab company. Considering he came over looking for the land of opporunity and ended up living in a 1-room appartment, it's pretty much the only thing he has any pride in- and it's not great. When it burns down, he really goes nuts at Niko.
What does Roman want in life?
Titties, obviously. But apart from that, he spends half the game in a kind-of ass-kissey relationship with Brucie. Brucie's a hyper confident alpha male, and it says a lot about Roman that this is the guy he loves to hang out with.
Roman's insecurities are pretty clear through the amount of gay-jokes he makes, the fact that he goes to strip bars so much, and that he gives Niko a hard time about how he's dressed, how he looks, and that he's not meeting any girls. He's into gambling and drinking and strippers because his actual life is crap- which we can see in cutscenes. I'm not even saying this is deep-down psychology stuff, I'm just sayin this is what you can SEE when you play the game normally. He's a crude guy on the surface, but it's clearly to cover up the fact that he's a complete baby. Y'know- like how people in real life are.
Roman wants to be respected by Niko at the start of the game, but after a while he starts to think Niko is actually a maniac. For example; he's lieing to Niko about how many women he sleeps with on day 1, but after about 10 missions he says "You're here on some revenge mission for something that happened 10 years ago, and you don't care who's life you ruin on the way." before leaving you alone for a while to restart his company. By the end of the game, Roman talks to Niko like he's practically addicted to killing people. On one of the last missions he says "No more killing. I'm trying to start a new life here, let's just take this money and get out, you don't have to kill another person."
The way Roman builds his new company, marries that girl (not a clue what her name was), and is almost begging Niko to stop fucking murdering people is him growing up. There's NO DOUBT that he changes over the course of the game, for the better. We know what he's scared of, we know why he's here, we know everything about Roman the same way we know a real person. There is at least a couple layers of depth to this character between what he thinks of himself, and what he wants Niko to think of him.
NIKO, on the other hand...
Niko meets up with Roman, and I think his 3rd mission is to stab some dudes to death, and his 4th mission is to throw a brick through a guy's window. It escalates, and y'know, he couriers drugs and robs a bank soon enough, kills basically a million dudes without ever saying no, and dives head-first into the mafia. His excuse is that he does it all to get closer to the guy he's after-- but come on.. You don't kill a million guys just to track down 1.
He kicks the shit out of anyone who goes near Roman; gets him kidnapped, gets his business burnt down, and thinks very little of anyone you make friends with in the game. Except Packie, I think.
I never really got a sense of Niko's personality, except for that he won't stand for shit, will pretty much go with anything, and makes friends easily. He talks about his backstory a lot: He joined the armed forces really young and saw some real bad shit. He saw the world while he was in the navy, and really doesn't like America. He has more pride than Roman, but zero morals. He talks down to every character in the game, and doesn't grow up or learn any lessons for the whole story.
This is without mentioning that he roars out loud when you fire a machine gun. I think he's a mug, with as much personality as a brick. I'm bringing this up now, because GTA 5 is a thing, and I think most people remember liking Niko and hating Roman.
It's fine to hate Roman as a person, cos he's not likable, but I think he's a way better character than Niko. So I want more Romans, more Brucies, more of those biker guys, and no more Nikos.