The saddest part about Grand Theft Auto IV is that it had the best writing of any GTA game but the game itself overall kind of sucked outside of the story and writing. The driving mechanics especially sucked ass and there wasn't much to do outside of the story missions. Weapon and clothing choices were also extremely limited.One thing I really like about IV is how nuanced it is, compared to nearly every other Rockstar game. RDR2 had rather good character and (sometimes) thematic writing, but fell flat in regards to social and political writing. GTA IV, on the other hand, already starts off with funnier political satire. Then, the main thematic element is definitely the American dream and immigration. You'd expect the story to go full on "America isn't any better than Serbia and Niko is completely innocent", but it instead examines whether Niko contributes to his circumstance in any capacity. He didn't like working at the taxi company at all, and he felt a compulsive need to be violent (a very obvious commentary on the player), so he kept pushing situations further and further past the several points he could have willingly stopped. Then, after the game ends on a rather nasty note and scrutinizes the typical "rise to the top" GTA story, it still heavily implies that Niko can still put this all behind him and accept a decent lot in life. It's shockingly good writing on Rockstar's part, and the only game that comes close is the best parts of Max Payne 3.
Don't get me wrong, GTA IV is good but it's also a game of extremes. It has the best story and writing in the series hands down, but in terms of gameplay, it's one of the weakest in the series, especially since San Andreas was so massive and detailed by comparison and even Liberty City Stories and Vice City Stories seemed more fun and complete than IV did at times.
That's part of why it's sorta controversial within the GTA fandom and why "IV vs. San Andreas" threads were such a big deal on places like GTA Forums up until GTA V came out.