Anecdotal reports here (or on any enthusiast site) are probably not the best way to judge a car. One the one hand, you'll have people who love the car and will defend it vigorously. On the other, people who have had problems will search out sites like this to seek guidance or complain and appear in greater percentages than the general population.
You'll also have people in the middle like me, but take it from someone who has been visiting sites like this since the mid-90s, the two ends of the bell curve will be fatter here.
All that said, my thoughts about the car are as follows: it's the best (and only) drivetrain to fit my needs and I like the car's design and styling, but fit and finish are not what I'd expect on a $40,000 car.
If you are looking at the Volt, then I don't need to sell you on drivetrain. Full electric is not close to being ready for primetime in my area and with my occasional need to drive long distances. I like the styling to the extent the car does not scream "look at me" and I think that I'll enjoy driving it for a long time (I keep cars much longer than average).
I've been disappointed with the little rattles and misalignments of panels (inside and out) and even with the anecdotal bias noted above, I've been alarmed with issues some have had; "shift to park" being the worst. To be sure, I have not experienced any operational failures aside from two instances of "remote not detected" in 12,000 miles of daily driving.
As for GM customer service (both at corporate level and at the dealership), I can't really give an opinion. I have not needed to deal with GM corporate and aside from the expected general cluelessness re: the Volt at the dealer service center for a couple of TSB campaign visits, I have not had a problem there either. Except for warranty work, I almost never go to dealer service centers so that is not a factor for me.
The bottom line for me is that even with the fit and finish issues and the "shift to park" issues some others have had, one year in I would definitely purchase the Volt again. It's the only car that fits my needs and I think the warranty coverage is good enough that any serious problems will be dealt with should they arise.