I've been on nix for only 2-3 days so take what I say with a grain of salt. I think it's pretty useful. Back in Arch/EOS, I always find ways to mess up the system (I switched to Nix because of a failed system update on EOS). On Nix, it's so easy to roll back and you don't even need to use the terminal.

sudo nixos-rebuild switch --upgrade

There are (afaik) 3 channels you can choose: stable, unstable, and small(?). I'm staying on stable for now. Package manager is slower than pacman, imo, and it's not as straightforward as Arch. Some programs (like kde connect) need to have service enabled in config.

Yes

So how useful it is in practice?

It can replace the need for docker.

Replit.com uses it for its VM environments. See: https://blog.replit.com/nix

So how useful it is in practice?

It's useful for quite a few things in practise:

• You can be sure software that is packaged with nix will behave the same on different computers.
• You can avoid dependency conflicts.
• You can automate some things that would otherwise take multiple (mostly manual steps) on other systems.

This video shows off some of the cool things you can do with nix: https://youtube.com/watch?v=6Le0IbPRzOE&feature=share9

How do updates work?

You update a programming by specifying the latest version of a program in config and rebuilding.

You update the OS by pointing to the channel you want to use and rebuilding.

You can time travel back to a previous state if anything goes wrong.

Can it play Crysis?

I expect so, some people.do use nix for gaming.