There are different ways in which different players are great.I am new to watching hockey actually. Just started 2 years ago and only started trying to understand and learn about it in greater detail this year. I haven't yet been able to figure out how someone is considered good vs great. Bad players are easier for me to spot though.
Some have almost exclusively a great offensive game, maybe specifically their shot or their ability to make plays.
Some players are extremely gifted as defenders- this may be a little bit less obvious when you watch it. But you will start to see some of the little things great d do.
Goalies, well, most of it comes down to positioning. A great goalie these days has almost perfect positioning to where the puck is, and can anticipate to a high degree where it will go.
Good players are good at these things, but you'll see the difference in their games and on the stat sheet. Usually.