I can't speak on 1 or 2 because I honestly never played them.
I love III for how it perfected the open world concept and I still love it's vibe.
I love VC for the 80s Miami Vibe
I love SA for it's 90s west coast vibe and just how huge it feels even if it's size is just a programming trick
I love IV for the raw and gritty NY vibe and how dirty the criminal acts feel. You can almost smell the pissy stairs in the projects
I love V for the LA vibe and how action packed the missions are. I also love how Sandy Shores just feels like the wild west.
I love them all. Am I the only one?