GTA IV holds a special place in many gamers lives, as it was the first GTA game on HD consoles. The story of Nikko Bellic coming to America and getting involved with the criminal world of Liberty City still holds it's own, even against the antics of Micheal, Franklin, and Trevor.
Sure, there are things in GTA IV that haven't aged as well. Mission checkpoints are nearly nonexistent -- making you restart missions from the very beginning if you fail, car controls feel more stiff compared to other titles, and Roman can get downright annoying. That said, the world, gameplay, and storyline are still worth playing. In addition, seeing how improved Red Dead Redemption was when playing it on Xbox One, it would be amazing to see what Microsoft and Rockstar could do with GTA IV to make it a better game.
I love GTA V. It's one of my favorite games and one of few open world games that lasts 30-40 hours that I can replay over and over again for so many hours. But sometimes I love to go back to past installments and see how much has been improved, while experiencing the story over again.