I am skeptical any ISP will provide me enough bandwidth that you can stream to me without it being a painful experience.
I have been using the beta of this service for quite awhile now (on cable internet from Charter Spectrum). I haven't seen any image degradation and the input lag has been, at most times, imperceptible. The frame rate has been maintained at the promised 60fps, and the graphics settings have always been at Ultra/Maximum (something I couldn't accomplish on my own hardware without some costly upgrades). It may not be 4k, like Google's offering, but it has been more smooth and reliable by several magnitudes (I've tested that services as well). I don't know what wizardry nVidia has done to get it to work so well, but it's like magic. Also, not having to re-purchase my games on another platform just to stream them is much more appealing than the economics of Stadia.
Doom Eternal?...I am skeptical you could get good detail levels and frame rates at a latency level low enough for me to actually play it
We obviously don't have Doom Eternal yet to test this but it's id Tech 6-based predecessor, Doom, runs smoothly and looks great on the service so I have high hopes.
In answer to the question of who this product is for? I'm a Mac user who also built a PC just for gaming. Lately, I've been finding myself loading up GeForce NOW on my Mac more and more, rather than dealing with the slight hassle of switching my monitor source and input devices over to the PC just to do some gaming (even though its basically just three button presses away). I have spent hours trying to set up and optimize the various LAN-based game streaming features via Steam and GeForce Experience to try and stream games from my PC to the Mac sitting right next to it over gigabit ethernet, and even that somehow doesn't seem to work as seamlessly as GeForce NOW. Until Apple and nVidia settle their beef and I'm able to just install a proper high-end graphics card in my Mac, I'm sure I'll be willing to settle on this solution. Heck, even if/when that comes to pass I'm sure I'll still find myself using the free tier to do some gaming when I'm not at home.
Prove me wrong NVidia! :)
Guess what... there is a free option so you can try it out and find out definitively if they do!