Sony is often criticized for using a similar design on the hardware of their flagship devices. The OmniBalance design language was introduced with the Xperia Z, and it was based on symmetry in every direction. It featured glass in front and back and a shiny round power button among other metallic elements, making it look quite elegant. Even more impressive was the certification that made that phone waterproof and dustproof that has been present on every iteration that succeeded that phone. Sony made a picture showing some changes on their flagship phones over the years.
The Xperia Z featured a 5-inch display with Full HD resolution and the design was flat on the edges. For the Xperia Z1, the company introduced a 20.7-megapixel camera sensor and a physical camera button on the side, while it used the same screen, it was a little larger and it featured more metal on the frame and it was slightly rounded towards the edges. The Xperia Z2 featured an all new 5.2-inch IPS display with Full HD resolution, improving the viewing angles and color reproduction as the previous phones didn't receive such positive reviews on this aspect. The design of this phone was similar but the frame holding the glass on front and back was almost entirely made out of metal, only some polycarbonate was used towards the edges. This was also the first time that front-facing stereo speakers were used in the series.
On the Xperia Z3, the frame surrounding the device is made entirely from aluminum and it's completely rounded, but the four corners are made from nylon. While the screen was kept the same from the previous version, the phone is actually smaller and the camera sensor had ISO 12800. For the Xperia Z3+ (known as Xperia Z4 in Japan), the company used an almost identical design, but the frame received a special treatment making it shinier while enhancing its grip, for the first time, the Micro USB port was uncovered while retaining the IP68 certification against water and dust.
Sony announced the Xperia Z5 earlier this month, and while the design is still recognizable, the metallic frame uses a less rounded shape, the power button has been resized and reshaped to accommodate a fingerprint sensor for the first time and the volume rocker and camera buttons have been repositioned so that the finger rests there more comfortably, the back of the phone is still made from glass, but it is frosted this time around, providing a matte finish less prone to fingerprints. The 23-megapixel camera sensor is also new and it features the fastest autofocus in any phone.