A Good game is fun to play and is a good time.

A great game you don't realise 5 hours have passed.

Good 8/10
Great 9/10
Masterpiece 10/10

Dark Souls 3 to Bloodborne, thats the best example

Usually attention to details and not just going the safe route.
Also I would say if it is a great game I will probably think about it several times afterward and probably replay it. Good games I probably enjoy when I play them, but might not think about them a lot afterwards.

Great : Final Fantasy IX, Mass Effect 2, Jagged Alliance 2
Good : Dragon Age Inquisition

A great game is one you can replay a million times and never get tired of it.
A good game is one you can play once or twice, feel satisfied but not want to go back to it.

Great means "of ability, quality, or eminence considerably above the normal or average."

A good game is fun to play and well-designed. A great game shares those qualities but in a rarefied way.

No need to overthink it.

Following internet wisdom: Graphics.

Being BOLD. Sure you can make a decent game with a checklist and tons of work and testing. But being AWESOME, GREAT, UNFORGETABLE takes daring, boldness, a little bit of optimistic naivette even.
Like, the old saying: Not knowing it was impossible, they went there and did it.

I like so much all these answears I felt they needed to be quoted.

Their all true.

The difference between Galaxy and Galaxy 2

:p

But Great > Good, different standards for different people, but I would say a Good Game would be on average a 7-8/10 while a Great game is 8-9/10