The processor, screen size and resolution, and case materials are all big upgrades over the 2013 Moto X my wife has. (brighthand.com)
The other big upgrade is the integrated Wi - Fi and Bluetooth that took designers a year to incorporate while maintaining the same form factor as previous models. (treehugger.com)
An SSD is the single biggest upgrade you can give your computer, and prices have come down dramatically. (howtogeek.com)