Apparently there's quite a lot of buzz about the ring going on.
Honestly, in Kate's place right now, I would be unbelievably honored to have been given that engagement ring. One thing there was never any doubt about was Diana's devotion to her sons, and their adoration for her. For William to give Kate that ring says, to me, that he holds her in just as high esteem as he did his mother, and I think that's wonderful.
I guess what I'm saying is, I think it should be viewed in terms of its meaning and importance to William, rather than what it may or may not signify to the general public.
Also, regardless of what happened in their marriage, I think it's safe to say that when Diana received the ring, it made her very happy, and this is a way for Kate and William to share that happiness and, hopefully, continue it.