Yeah I started on the Civ series way back in Civ I, and for my money Civ V is now far-and-away the best overall game in the series - which surprised me because I loved Civ IV and prior to Civ V's actual release I always thought a new civ game would be a bit pointless.
When it was released, it was a mess of bugs and sloppy implementation and lack of balance, sure - but the underlying core was great and I always thought it had amazing potential if it just got polished up. And it has, thanks in large part to Thalassicus' balance mod paving the way, but also full credit to Firaxis for actually being prepared to go back and make large-scale changes to the game to get it where it ought to be. The gameplay balance in particular is now much, much tighter than it was, with only a couple of significant remaining issues (really just the research agreement/trade gold issue). Diplomacy and AI are still a bit wonky, sure, but they're perfectly workable now - and let's be honest, how many of these sort of games actually have good AI anyway? I quite like the more aggressive, backstabby nature of the AIs - keeps you on your toes - but I can see how others might differ.
So yeah it's at the point where it's really more about whether you prefer the design decisions of the previous civ games, or the new design decisions in Civ V. Some people hate the new direction, and so will never be happy with Civ V - fair enough. I personally think the new mechanics are almost universally fantastic improvements that offer a wealth of big-picture strategic options while mostly avoiding the tedious mire of rote micromanagement masquerading as depth that plagued some of the previous games. I gather it's on special at the moment, so if you find it at all interesting, I'd say it's certainly worth trying out.
And as others have mentioned, a game that still has such a huge number of people playing it a year after release is a pretty rare thing, so I'm clearly far from the only one who feels that way about it.
