It's basically Intel's FX 9590, trying to push the absolute most out of an aging architecture/process power consumption and temperatures be damned, all because they can't get their 10nm yields up to acceptable levels. About the only thing going for it is unlike the 9590 it actually is a good performer despite the power and heat issues, but at its current price it is a hard sell. As a pure gaming chip, it's barely faster than the 9700k or even the 8700k once overclocked because virtually no games scale past 6 cores/12 threads right now. As a productivity chip, it's sold at such a high price that you could get a 12 core/24 thread Threadripper chip for a similar amount of money once you factor in the high end cooling you also have to buy. The Threadripper chip would trounce the 9900k in most productivity workloads.
About the only situation where the 9900k might make some sense right now is if you are a Twitch streamer and you don't want to use GPU encoding or a dedicated streaming PC. In that one use case, the 9900k outdoes R7 2700x and Threadripper in terms of the balance between game performance and encoding performance.