I think that the question: what makes a good writer, is a terrific one, because it is so subjective. One person will claim that it is someone who’s grammar is impeccable. Another will say it is someone who can draw you into the story. Still a third will tell you that only someone who is an English Lit grad can truly end up as a good writer. Extraordinary. And, as I’m sure you’ve guessed, everyone is right. At least from their own point of view.
For myself, I think a good writer is a good story teller. I seriously will gloss over some fairly glaring grammatical errors when reading a novel if the story has pulled me into itself. I don’t excuse the errors, of course, but then I’ve never claimed to be perfect myself, so I tend not to expect perfection in others.
I’d say a perfect example is Dan Brown. Love him or hate him, formulaic or not, his stories draw you in and then take you along for a wild ride. That’s a good story teller.