There are fairly standard criteria for literary criticism that include psychological and social insight, use of vocabulary, use of advanced writing techniques, use of form, and many, many more.
It is all opinion, but there’s a difference between the opinion of Alan Kay and of someone who has two days of Python and a copy of Angry Birds.
Your example of Alan Kay isn't a very good one though, because we can objectively test their opinions on say, the best way to implement `malloc` by having them do it and testing the results against the computer. There is no such equivalent for literature.
It is all opinion, but there’s a difference between the opinion of Alan Kay and of someone who has two days of Python and a copy of Angry Birds.