The ASRock Fatal1ty X370 Gaming K4 is a complete motherboard for Ryzen CPUs. It is basically a budget version of the X370 Taichi, which is a high-end motherboard. The only points where it is behind the X370 Taichi are the number of SATA-600 ports (six on the Gaming K4, ten on the Taichi) and the voltage regulator, that brings 16 phases on the Taichi and 12 phases on the X370 Gaming K4.
Besides that, it brings all the features offered by the high-end chipset for the AM4 platform (the X370), like the ten USB 3.0 ports, two USB 3.1 ports, eight SATA-600 ports (two of them available on the M.2 slots), and the compatibility with SLI and CrossFire with two video cards.
The motherboard has a high-end audio section and it will satisfy even the more demanding users, with its high-definition codec, gold plated analog connectors, and headphone amplifer.
For all of this, the ASRock Fatal1ty X370 Gaming K4 is a motherboard with great cost/benefit ratio if you are building a computer using a Ryzen CPU.