I loved Civilization III. As a young adult I'm not sure I really grasped a lot of the complexity, but I still played it endlessly, likely on an easier difficulty. It was my first real introduction to strategy outside of the Age of Empires or Warcraft style.
For some reason I never got around to playing Civilization IV. I owned it (on multiple services), but have just never played it. When Civilization V came out, I, along with most people, got absurdly addicted to it. After many many weekends and days off completely lost, I had to stop playing it. I still bought the DLC and I would spend a few weeks every six months playing it, but always had to force myself to stop, lest I lose any social life remaining.
Gods and Kings is incredible. It tweaks a lot of the things I wanted tweaked, adds some cool civs, and introduces some fun new mechanics. I'm addicted to Civ V again, and it's awesome.
Every once in a while though, whether its in the comments section of a review or on these forums, you'll see that guy who loves Civilization, but hates Civilization V. They see the streamlined UI and graphics as watering down their favourite franchise. Perhaps this is valid, perhaps it's not. Civilization V has clearly innovated in areas that allowed it to be accessible to people who never grasped it before. These people often cite Civilization III or IV as the pinnacle of the series (seemingly 50/50 split there).
What I'm wondering is, to someone like me who has played III and V, is there any point in trying out IV? What is it about IV that gets people so excited?