I do not know if I agree with Rupert Christiansen's decision to rank Debussy's Pelléas et Mélisande as his favorite opera; but, except for the ghastly visual pun on the Telegraph Web page, I found his appreciation of the opera an excellent and stimulating piece of writing. I suppose this is because I think he makes a good point in justifying his choice:
Opera is too often stuck in the art of the crashingly obvious, painting emotions and situations with a broad brush. Pelléas, on the other hand, is endlessly subtle and indeterminate.
I, personally, have seen Pelléas twice, once at the Met and once at San Francisco Opera; and I was blown away by both productions. I would also argue that, in the case of the more recent San Francisco production, there was real value in displaying the titles. Given that, regardless of language, most opera singers end up short-changing their consonants in the interests of both being heard and sounding musical about it, unless you have memorized the libretto in its entirety, you cannot follow the text on the basis of what you hear; and subtlety of language (handled so well by Debussy) is a critical factor in this opera. The San Francisco titles demonstrated that this subtlety can survive translation; and, as a result, I both heard and saw far more in this production than I did in the old title-free production at the Met.
So, if I do not agree with Christiansen on the bottom line, am I willing to stick my neck out and declare my own personal favorite? He has not made it easy with his choice of criteria. I am always hearing new things in Wagner, but I would agree with Christiansen that the Wagnerian brush is pretty broad. For me, however, the ultimate in the "subtle and indeterminate" is probably Mozart's Così; and Mozart does not have to resort to symbolism! Ultimately, this is an opera about the complexity of the human heart; and that complexity is so extensive that the stage director has no explicit cues as to how to end the work! As a result, I have seen as many plot resolutions as I have seen productions and have no desire to classify any one of them as "better" than the others. There are only six characters in this opera; but I could probably spend a lot of "desert island" time plumbing the depths of character in each one of them!