The Moto X is still rolling out to all corners of the (American) Android world, but the T-Mobile variant is getting an update that improves camera performance dramatically. The difference is noticeable in a variety of situations, most notably in backlit and low-light settings. Presumably the update will hit other Moto X variants once testing and certification is completed by the carriers.
Low light – left: not updated, right: updated
The Moto X uses a fairly large sensor with 1.4µm pixels with an RGBC color array and F/2.4 aperture.