For me (a semi-geek, I suppose you might say) a great brewery is one that consistently produces great beers, and makes producing great beers their number one priority. And also all the usual stuff that would make any company "great" - well run, good working conditions, ethical supply sourcing etc. etc.
Don't really know enough about any brewery to decide if they qualify to be called "great", but if they do all the above I don't think you can really argue with them being called great, can you?