Once I 100% V, there's nothing there that has any replay value for me (Multiplayer holds no attraction for me in any game), and will definitely be going back to GTA IV. As far as I'm concerned, despite the beautiful looking world and vast improvement on IV's clunky shooting mechanics, GTA IV is head and shoulders above V in terms of gameplay, story, atmosphere, humour and immersion. R* completely devolved the driving experience in V to Mario Kart car control and mechanics, the story is messy and without any direction, not to mention unbelievably short (some of the main missions can't even be considered as proper missions) that I feel R* sacrificed the Single Player experience which their games have always been based on, concentrating on MP.
GTA IV was epic in storytelling and gameplay, a Martin Scorcese or Francis Ford Coppola three and a half hour magnum opus as opposed to GTA V's style-over-substance 90 minute action movie - and to be honest, there was far more action in IV than in V.
IV also had three protagonists with an entwining story, it's just that you couldn't switch characters during gameplay. The humour was more subtle and amusing as opposed to the "slapstick" in V. I found Niko to be a far more engaging character, one that was easier to relate to and sympathise with, with a very dry sense of humour and an amusing aside. His dialogue and interaction, not just with other story characters, but peds, police etc was amusing.
IV had more memorable characters; Roman, Brucie, Yusuf, Packie, Tony Prince, and my favourite NPC, Little Jacob. There was a true cameraderie between Little Jacob and Niko that has never been bettered before or after IV. In V, the only character that truly stands out is Trevor, but other than that, most are forgettable.
I wanted to love GTA V, I wanted it to be better in every way that IV, but having played it I feel it was grossly overhyped and didn't live up to my expectations. R* dropped the ball on so many things in this game and I'm astonished with the end result, bearing in mind that it was postponed a year because R* wanted to "tweak" it to make it better - and this was the result? It is a very good game, with many interesting and novel features, but sadly it could have been so much better than it is.
So yes, I will be returning to, and continue playing IV, to get the bitter experience and sour taste of the driving physics out of my mouth until GTA VI comes along.