Meh... while the sensor size is larger when you account for the higher number of MegaPixels you find that the pixel density of the 20 MP sensor is higher than that of the 13 MP sensor. Higher pixel density is bad for image sensors since they will generate more noise in low light. So unless they are doing some supersampling like Nokia and effectively increasing the area of each pixel I'm not too sure this camera is going to be much better than that of the Xperia Z line.
Also the lens is still an unknown but that can make a huge difference as well. from the picture though, it looks like its pretty packed in there so I don't think they can improve on it much when compared to what they used in the Xperia Z save for maybe some OIS (optical image stabilization)
Either way the specs are still awesome, was just hoping for a bit more from the camera. But who knows maybe I'm jumping to conclusions too early.