The city feels dead
I think my biggest problem with this game is the city of Los Santos - more specifically, the pedestrians.
I'll start with the fact that while it is a very well-designed city with some really cool places to explore, it simply lacks. There are next to no interiors (I know, the interior discussion is another debate altogether, but there should at least be one or two cool explorable places).
What makes it feel so dead is the people. None of the pedestrians make you feel like you're in a real city. They all have a certain stereotype to reflect they're surroundings, same with Liberty City in 4. But apart from a few funny overheard comments, that doesn't necessarily do anything to make the environment feel more immersive. Not to mention the noticeable lack of pedestrians in a lot of areas.
I don't know if this is just because rockstar was focused on the environment outside of the city and didn't think it was really a big deal - yeah, there's an obligatory city to explore but the real draw was the massive mountain, forest, and desert areas. Or maybe it was part of a bigger plan to downplay the brutality you could inflict on innocent people by making them seem more like space fillers than actual citizens of a city (although I feel like that doesn't really make sense with the additions of the hammer and hatchet, along with everything else you could already get away with). I'm not sure, I just feel like to me one of the best parts of GTA IV was that the city felt so real and the abundance of pedestrians who all had something colorful to say. GTA V is an incredible game, don't get me wrong. But I have always had the feeling that the city and its citizens are lifeless and somewhat boring