I love Niko to bits. Even though his name is as unsubtle as it gets. "Niko" sounds Eastern European, but is not an actual Serbian name. It comes from "Nikovo", Russian (Niko is a Serbian, mind) for "Nobody". "Bellic", is from bellicose, or just "war" (Latin: Bellum, i think) in general. Nobody from the War. That's him. That's a miserable, arguably suicidal, crestfallen, self-loathing, fatalistic, nihilistic, but noble cynic. Noble, in that he feels obligated to protect the very few people he finds himself drawn to. It's like some murderous but not-quite-completely-evil revenant of some horrifying event (Yugoslav Wars).
Problems are:
1. There's nowhere for him to go, no self-betterment possible, no dream to struggle towards, no victory to achieve. He acknowledges as much himself. His story as a human being ended with one of the most inhuman conflicts of the 20th century.
2. He's a genuinely awful person in most of the ways that count, but he is definitely not the type fit as an open-world crime game protagonist. He's far, FAR too reserved for that. He may kill you if given a reason (money being a good enough one, usually), but he's not going to just flip out and initiate Operation Blaze of Glory.
Thus, GTA IV had a decent-ish story with a decently written (I thought) protagonist, and was also incredibly jarring.
Oh yeah and BIG AMERICAN TITTAIS gets annoying after a while.
Driving without mods was shit too.
Maybe it was just not a great game.