I was one of those people who loved Civ 4, then bought Civ 5 on release day and got bored with it by the end of the week. I briefly got back into it when Gods and Kings came out, but it still wasn't enough to really hold my interest.
Brave New World, though? I preordered it on a whim the day before it came out, and now I can't tear myself away from it. Trade routes and more involved cultural mechanics, along with the espionage and religion from G&K, are just the right mix of complexity and choice to keep things fun.
Simply put: it's good. REALLY good. If you didn't like Civ 5 before (and I didn't, as I mentioned before), this might be enough to redeem it in your eyes. I'm sure yet if it will supplant BtS as my favorite Civilization game, but it's pretty close.