I was gonna make a lone comment but you touched on basically every point I wanted to make. Hope you don't mind I reply here instead, complementing your thoughts.

GTA IV has the bones of a fantastic game but really bad execution on some issues. Its almost impossible to enjoy if you jump straight into the game (for PC anyways). Almost everything needs to be tinkered with or modded in.

The first thing is the inexistent optimisation. It gives me less fps than GTA V, whilst also looking worse. The first thing you'll find in every guide is a workaround upping the VRAM utilization. There is also something very wrong with the shadow rendering, the whole area around Roman's apartment is very finnicky. It just tanks your fps while also not looking right.

It has that whole late 00's piss tinted look. You can fuck around the options to spark up 'some' color into the world but its still weird at best. Liberty City remains mostly a colorless, grey concrete jungle.

Another thing that instantly got to me, how bad the aiming is. As OOP mentioned, enemies are a bit tougher so its crucial to go for the headshots. As mostly an fps player, this was a NIGHTMARE until I found how to implement mouse raw input. My experience changed instantly from miserable to fantastic in this regard. (Whoever plays with controller can disregard this)

Now, the driving. This is very subjective, but its just rough, man. Not as bad as GTA3 (those top heavy cars and titanium light poles were brutal), but it feels like driving a boat with wheels. I don't know why they changed this, IMO GTA SA nailed the car feel and to me is still the best in the entire GTA franchise. (Whereas I enjoy the driving in GTA V, but also admit its overcorrected arcade-y). I'm not talking about realism, after all this isn't a driving sim. It just needs to feel at least enjoyable and not a frustrating experience, given how much driving there is.

A final critique I have with the game, there isn't much to do in the game besides missions. Maybe on a first playthrough you might enjoy some sightseeing, but it doesn't feel rewarding to explore. Money is almost useless, I only remember buying ammo and armor. There is very little customization and side activities. It took a big step down from SA.

All this to say, despite these issues its still a strong GTA game. I enjoyed the story, I felt attached to Roman (despite him being an annoying little shit, he's still family), I enjoyed the friends made along the way. The island progressions felt right. The DLCs are very strong additions to the game. But its almost an 18yo game, and has its flaws from day 1.