Ryzen isn't an upgrade over anything Haswell-based or more recent, except when you need more cores (Pentium and i3 owners would see a boost). You wouldn't get better performance in current games if you left the Ryzen at stock, and overclocking it is still tricky. You'd have better luck replacing the GPU, as it stands.
If, however, you're sure that you're CPU-limited, then Ryzen would be a good choice provided you're ready to spend more on cooling and RAM, track BIOS releases closely and generally babysit your computer: an overclock to 3.8-4.0 GHz would indeed bring a 20% improvement in CPU speed (provided you feed it good RAM) but many games are still far from being optimized for Ryzen leading to artificial slowdowns.