For the last few years digital sensor improvements have been slow but steady. Its hard to find a bad camera today.
The latest buzzwords are Back Side Illumination and Stacked Sensors. The Nikon V1 was one of the first cameras to use the new BSI sensors, but what does this mean.
In a typical sensor you have the sensor pits, but the available surface area has also to be shared with the supporting electronics, reducing the area for light collection. In full frame sensors and medium format the area lost is inconsequential but as the sensor gets smaller the percentage area lost increases. BSI and Stacked sensors, basically moves more of the supporting electronics underneath allowing more available area for light collection.