GTA IV was a damn great game. People on the internet are just loud when it comes to hating something popular. Everybody I know in real life who played GTA IV loved it.

If we are talking about entertainment, quality is subjective.

I have the strong feeling you haven't played "every Mario/Zelda" though.

You got me there. I haven't played SMB2 or any nes/snes zeldas. I saw some zelda game on nes and I had absolutely no interest in playing the game. First zelda I played was Ocarina of time or majora's mask and after that I tried Link's awakening on GBC and Link to past on GB(A?).  I've also played TP,WW,Phantom Hourglass and spirit tracks. I guess that is enough to know that those games aren't any good at all, IMO.

and don't bother listing all mario spinoffs, I haven't played all of them

The only person you must know is Antabus then

Yes, I concede, I enjoyed it. I was just fully disappointed with its level of realism, unlovable characters (aside from Roman who I killed off anyway), and its lack of sidequests.

Just seems like a step back in general really. Or maybe I just expected too much

You were expecting too much. Compared to other sandboxes this gen GTA  4 has the most things to do other than the main quest. And also a huge city which I can access without loading.

Is it overrated on metacritic? Sure. Is it a bad game? Not at all, it one of the best sandbox games this gen.

Yeah, but only Red Dead is up against it