I loved A SWIFTLY TILTING PLANET too, and still re-read it every few years. And I don't think L'Engle meant Matthew's portrayal to be at all negative, as he's such a compelling and sympathetic character. It was more that I was annoyed at Zillah for not seeing how much Matthew loved her, how worthy he was of her love on every level, and how unfair the whole scenario was. Plus, there are so many other books where the PWD character doesn't get to live a full and happy life or love and be loved in return (unless, of course, he or she can be magically healed first)... it was just a last-straw kind of thing for me.

But hey, it kickstarted me into writing Knife, so I am forever in L'Engle's debt in that respect.