> what makes a great gaming machine?

A piece of hardware that runs a basket of popular higher-end games at close to 60fps is generally what people look for. If you know you wanna run DF you can use much cheaper hardware, but if you wanna run "games" you wanna check that your target pc performs good enough on a selection of games.

What makes a gaming machine...

Good - at parity with a PS5 Pro or XBSX in the latest AAA titles.

Great - better than PS5 Pro or XBSX in the latest AAA titles.