With the recent announcement that the Xperia Z series is no more, a new line has to take its place. That is where the Xperia X series come in. They look similar to the now-former Xperia Z series, but with more ‘smart' features. And the phones will be sold in the United States, a path of distribution Sony hasn't fully committed to in the past.
Sony has released an infographic showing exactly what makes an Xperia X phone “smarter than your average smartphone”. Some of the reasons include things like the camera having Predictive Hybrid Autofocus, much improved battery management that Sony says will let an Xperia X phone last up to two days on one charge, and improved look and feel. Although, I'm not really sure if you can consider a phone looking and feeling better as being “smarter” than other phones.
Source: Sony
I find the X series to be underwhelming at best.
I don’t even see a difference from other ones