Graphics are excellent, I was running on Ultra RTX (remember, 1080p) in most of the city and getting 50 fps, and latency was around 20-30ms. For how most games play, it wasn't really noticeable. $5 a month is a great deal, though I do wonder how Stadia stacks up. I certainly could have used the better resolution.
It also works on iPad/iPhone and Android decently, if you want to play anywhere. I didn't have any issues trying my iPad, though it appears you're stuck with controller input on that.
I subbed for a few months and have never played CP2077 but here's the high level overview:
You buy games on Steam/Epic/Ubisoft game store as normal.
In the GeForce Now client, you pick the game you want to play (and on which storefront). When you "launch" it, NVidia spins up a VM, configuring it to launch the storefront you selected with your game, and connects a remote stream to your local client. You sign into Steam/Epic/Ubisoft (usually only needed the first time per storefront), and you "install" the game and play it.
It works pretty well. If you don't have cutting edge hardware and don't mind a few ms of latency, it's a pretty good deal.
Only caveat is that I would not use it to play shooters that require quick reflexes.