Some very well thought out posts here.
Personally, I think there's a question underlying that's not been asked – "What makes an artist?" is different to "What makes a successful artist?" An artist is someone who creates art, and understands their craft. A successful one earns a living from their art.
As for what makes art – all I can say is that everyone tries to come up with the "Thing that people like" as a way of hooking into the audience, tapping into people to make them like you.
But that is not what you need.
See, the artist is both audience and artist. If the artist makes art for the audience it belongs to (very different to making art for oneself) that audience will respond.
The smaller the audience, the less 'success' in terms of money and acclaim.
But that's really not what's important.
My suggestion to anyone in any art form wanting to succeed as an artist? Be good. Don't worry about audience, subject matter, or any of that nonsense. The greats create new audiences and genres that didn't exist. It's not about that. Just be good. If your quality is high, it will draw an audience.
And to be good, to have high quality, one must study the craft of their art. In story telling, that's studying and examining turning point, climax, character, and all the other aspects. In illustration, that's understanding the tools – pencils, inks, brushes, photoshop – understand how icons work, composition, and all the other aspects.
It's hard, but in my opinion… trying to work out what people "want" is a futile distraction from trying to be better.
What people want, as always, is something good. ^_^
And now that I've preached, I'll step off my high horse.
