The 24mm wide-angle view (in 35mm equivalent) of the 12mm f/2 lens makes it an ideal lens for landscapes and interior shots, where you need to see more around you. While a wide-angle lens can be used to shoot portraits, you'll need to watch out for the distortion in perspective that it creates.
When shooting with the 12mm, we see vignetting around the edges from f/2 to around f/4. We hardly saw any ghosting or flaring artifacts. It also exhibited good sharpness from the center to the edges of the frame. There is slight barrel distortion for which you'll have to correct during post-production, but all things considered, this is a very likeable, if pricey, lens.