From Leap Motion's developer blog:

V2 retains the speed and positional accuracy found in V1, but the software also now tracks the actual joints and bones inside each of the user’s fingers. This leads to some immediate benefits over V1:

• Finger and hand labels – every finger, hand, and joint now has anatomical labels like ‘pinky’, ‘left hand’, and ‘proximal phalanges’
• Occlusion robustness – fingers are tracked even when they’re not seen by the controller, as might happen if you turned your hands completely vertically or intertwined the fingers of your left and right hands
• Massively improved resistance to ambient infrared light – sunlight, powerful halogens, etc.
• Much more granular data for developers about the user’s hands and fingers – 27 dimensions per hand, in addition to special parameters like grab/pinch APIs