GTA V surpassed IV in plenty of ways, however I think I made more memories on IV.
That and if you try to get back into public GTA V now you'll probably be constantly killed by players with better items.
GTA IV is somewhat nice in the fact that every time you join a game you start back at square one.
However, I don't really see myself going back to IV. Especially with the popular custom servers on V.
I used to play it a ton. Now I find most servers to either be foreign, or left for dead.
A few gamemodes are still popular, such as StarWarsRP and HogwartsRP. Community is still just as autistic, which is a plus.