The Xperia Z went through six different version without changing very much at all. In fact it's probably fair to say that Sony caused itself far too many problems by iterating its flagship too quickly. The basic concept was good - a powerful, waterproof phone with a top quality camera and a very lightweight Android skin. The execution was less so.
Now the Z is dead and Sony has moved up the alphabet to the X, where we currently have three models: the entry-level XA, the mid range X and the high end X Performance.
Today we got the XZ. This is so very similar to the X Performance that you have to question why both phones exist. The XZ has a bigger screen (5.2" v 5") a larger battery (2900mAh v 2700 mAh) and a new sensing pack for its camera which combines IR and laser focusing and a second image sensor for depth / focusing / movement detection. USB-C replaces micro-USB and there's a new blended bevel design to set it apart from its stablemate.
It isn't the Xperia Performance that it will be competing against though.
Given that the phone ships with a 1080p screen, rather than QuadHD, one that also lacks AMOLED, that it still lacks OIS and is likely to suffer from Sony's inability to deliver high quality image processing on its own handsets, the suggestion that this is a handset that will compete at the premium end of the market with the S7 or iPhone seems something of a stretch.
Still, there's no question that Sony builds a good looking handset and this is as good as the best, for now. Sony's prioritisation of profits over volume is likely to make this a step to far for anyone who isn't already an Xperia fan, but for those Sony-philes this is probably going to be too good to miss.