Their reception in urban areas is great (but not excellent). Many of their plans now include Nationwide which means they piggy back off other carriers for areas where they don't provide their own service.
I have been with them for more than a decade because their value can't be beat.
The biggest negative for me is their customer service over the phone. Their operators seem to stumble at doing anything and have mediocre English skills. I try to do everything via their website.