As they are publishing essays on him then they take him seriously, but why do you assume they are all positive?
You *can't* assume that, for instance, Harold Bloom & Tony Magistrale appear under the same cover here:
http://books.google.co.uk/books?id=Y-vdjwEACAAJ
The National Book Award Medal for Distinguished Contribution to American Letters cannot be taken seriously as an award for literary merit. You don't even need to be a writer! Oprah Winfrey has won it, and the introduction explicitly says this was for her Book Club, not for anything she has written..., for being a good book seller. Does that mean Amazon or Waterstones can win it?
"A few college level syllabi" will include anything in this dumbed down age.
You can always find some critics say positive things about anything, even (especially?) in third rate colleges.
You *can* find some great critics who dismiss books that almost all other critics say are masterpieces.
But you can find many authors that almost all serious critics admire.
Stephen King isn't one of them.