First off, it's not an RPG. I wish people would get that through their heads, they changed that about a year ago when they discovered they couldn't deliver. People though are still stuck on that aspect.
That said, I've been rather critical of the game, and I will agree that the immersion part of the game is seriously lacking. That's the issue. It's not that it's an RPG or not an RPG, it's that the immersion is rather lacking. Just as you begin to truly immerse yourself in an aspect of the game, or a character, or a place, it's cut short and you're forced to move on. I mean take Panam for example. arguably the most developed secondary character in the game (I argue that Johnny is primary character alongside V). Just as you really get in with Panam, and become friends with her, everything comes full stop, and you might as well ignore her for the rest of the game.
Same with the Peralez's and their storylines and so many other storylines. Goro just disappears.