It's from some of the folks behind Lost, so if you liked Lost, you should know what to expect here. (This show's the reason I'm watching Lost).
It's also got quite a few other talented people involved like Jane Espenson.
As for where how good it is, it varies pretty wildly. I nearly stopped watching it until I got to Episode 7, so the first six episodes are… not bad but not particularly good either. Episode 8 is good, but then I started enjoying it less again up through Episode 11, which was probably the worst episode of the season.
And then they throw eight fantastic episodes at us in a row. And then the last few are okay, but a plot point it dragged on to groanworthy extremes, but overall, it ends well enough.
I recommend at least checking it out for that string of awesomeness there in the middle. It had been the highlight of my week for a good long while throughout the season.