DxOMark started doing selfie camera reviews a couple of months ago and it has already subjected quite a few smartphones to it. The newest addition is the Sony Xperia 5 but it got an underwhelming score for a flagship.
The overall score in the selfie department is 79 with a couple of noteworthy pros - wide depth-of-field focus, accurate exposure across all scenarios and good dynamic range outdoors. However, there's an issue with white balance, noise, dynamic range is rather narrow indoors. DxO also noted color fringing and less than ideal bokeh shots.
I have the phone and I can tell you first hand - The selfie camera is horrible.