The ultimate irony is, Red Dead Redemption 2 is more of a sequel to GTA IV for than GTA V was. Most of the criticism and praise of IV has been applied to RDR2.
Clunky or slow, unresponsive controls (which I do love, I don't want every single game to feel the same).
Story or narrative driven above all else, everything revolving around the story's themes is reflected in gameplay.
Excellent world building, unbelievable sense of time and place.
An emphasis on more realistic approached to more gamey things.
The main difference is, people were able to empathize and bond with Arthur, love him as a character and person. Niko was a very conflicted, broken, flawed person. Not much about him is lovable.
I do genuinely believe most people don't like Niko, over him being a terribly written character. The emphasis of people saying "he says he wants to change, BUT HE KILLS LIKE A THOUSAND PEOPLE!

", that is the ENTIRE fucking point of his character. He is FLAWED and a HYPOCRITE, two human behaviors and traits.
If you watch all the cutscenes, Niko is painted as flawed, and the emptiness of living in Liberty City exasperated that. You're offered a choice of killing a junkie or corrupt cop, both brother's to one of your friends. The main love interest after Michelle is the alcoholic sister of that same friend.
Roman is a loser, Brucie is a loser, Little Jacob is perpetually stoned, Packie is a broken and degenerate criminal.
The entire game is a depressing romp with absolutely no hope, with likable but fleshed out characters, depicting one of the biggest and most popular cities during W Bush era America.
Most of the criticism leveled at GTA IV about gameplay? I understand that, and on many levels, it's not addictive or fleshed out like PS2 GTAs. But everything about GTAIV is meant to be taken in as a whole. It is not supposed to be a larger than life, power fantasy experience. It's purpose is to be a depressing and cynical journey in a lively and believable world.
GTA V in so many ways felt like a game born from fans bitching and whining about GTA IV. I love GTA V as well, but it feels entirely reactive as a developed game, rather than having a strong creative vision from the start.
I've been a GTA and Rockstar fan since GTA III, I play these fucking games like they're crack. The common criticism thrown at GTAIV is generally lacking in any critical or deep understanding of the game.