You want to make a good game, you want to do something fun that you will like and hopefully people will like too. If you succeed in that, you have been good, maybe great for some. Of course I have an idea of what being a great game developer is. And you have an idea too or else how can you tell what you're doing is quality or not? How do evaluate your work is worth something or not?
So it sounds to me like your definition of what is "good, maybe great" is a game that the player, or the creator, finds fun and likes? Is that not true for every game that is released? Someone is bound to like the game or find it fun even if it is for reasons not intended by the developer. This also suggests that a game could be considered great even if the product was uninspired and technically basic, so long as it is popular. One such example is Flappy Bird, which can hardly be considered a masterpiece. If this is true, then it is no longer about skills or ability.
I don't believe I can objectively know that may game is worth anything just based on what I like and what I know. I can know if I like it based on what I enjoy. I can know if it conforms to technical standards; code that is efficient and stable, interfaces based on human-computer interaction and design principles, music and art I feel suits the style of the game and that I think looks and sounds good. This doesn't mean I am a great game developer, only that I've accurately used technologies and followed a process to produce a quality product. Many individuals and companies succeed in this way, but commercially fail, and they are not regarded as great game developers.
Sure there's subjectivity to it.
And there in lies the problem. If "great" can only be narrowed down to what people like individually, then there is no standard for what is great, and it is meaningless to ask the question. If you want to ask "what do you believe are the skills and qualities associated with game developers widely considered to be successful" then I could answer that for you, but this question is asking what skills make you great and "shine out from the rest" and I don't think there are any skills that satisfy that.
Why are Beethoven and Mozart among the most famous musicians in history with a respected musical legacy? Was it because they were organized, wrote nice sheet music, worked very hard? Perhaps they did, but there was obviously more to it, and to tell someone they just need to work hard and become a good piano player to be a great composer is a useless statement. You can speculate as to why they were great people; are people born with a creative genius, was it their upbringing, did they see the world in a unique way, was there something about their brains or their experiences or personality?
Steve Jobs is considered a marketing genius and a notably successful businessman, but he was widely regarded as an arse by those close to him. Why is it nobody ever considers negative traits in these types of threads? Why do people assume successful people must have behaved in a way that conforms with positive traits and ideals? I suspect that is because most of us only have a vague, logical idea of what we can do to help us succeed, but not necessarily what will lead to success.
We strive to achieve a quality standard, a level of greatness for our products that we get from our gaming education, looking at other people's product and noticing stuff that makes it great for us. We build ourselves a model, an ideal. Consciously or not. But its there even if you might think its not there. That's why I can tell (just like anybody) what's a great game developer from a less good one or a bad one.
If it turned out that a game developer you respect a lot actually just sat in his pants eating pizza during the development of his game while other people worked on it, would you still consider him great? How do you know that isn't the case? We can't truly know what these people are like or what their process is, unless we ourselves get to work with them. This makes me think that this thread is more about the quality of the product, and how that reflects the developer; Notch is now great because of Minecraft, Will Wright is now great because of The Sims. If this is how you define great, you still have the problem of subjectivity around what makes a great game. Are we saying Minecrarft and The Sims are great because of their mainstream success? This goes back to the Flappy Bird problem.