I bought the game during the steam sale, for $12.50 or somthing like that. I have enjoyed playing it, certainly I got $12.50 worth of value out of it!
I don't like it as much as I liked Civ 4, but when it is on sale, it is worth buying.
I will probably wait for the next steam sale and pick up some more of the DLC.
My own personal opinion, the game is pretty fun in the early stages, exploring territory, finding your enemies, deciding what your strategy is going to be, laying the groundwork for it, or failing to. That part is fun.
However it gets boring after that. I quit most of my games before they get to the modern era, it just seems to bog down into repetitive next/next/next where several turns go by before I really have to make any kind of real decision, and in the meantime it feels like a slog.
So I have played many games where I ran through to the late BC years and then quit, started a new game. In that sense I've had fun playing it--but with Civ V I used to frequently play the games out well into the modern era, if not to conclusion, because it felt like every turn I still had important decisions to make in the late game. With Civ V, even when the outcome is still uncertain, most mid/late game turns just feel like so much housekeeping, rather than the more enjoyable strategic/tactical thinking that keeps me engaged.