Yes I was somewhat vague. What I meant is primarily pacing. Much of the output of the new german school seems to me appallingly terrible in its pacing. I admit I am not very experience with opera but I find there are some monstrosities in the genre of programmatic instrumental music. I find that many programmatic composers mistaking linguistic narrative pacing with musical pacing as well as passages that serve a narrative role but are musically very out of place. Let me give you an example. The Dies Irae in Symphonie Fantastique makes absolutely no sense in the music except for its narrative benefit with its historical association. I also find in some tone poems of Strauss, passages that seem very out of place musically but serve a narrative role via lietmotif. This isn't to say that programmatic elements can't make sense. For example, Beethoven's bird calls in his pastoral symphony feel so natural to the music, since by way of proper pacing the music has led to that exposed open section. I find this culminating in much of Wagner's music. He might introduce an intense passage with a leitmotif that the narrative demanded but musically it feels out of place. Yes, I recognize that he is a master of his handling of motivic material. However it seems that the logic of the music takes a backseat to the narrative.
The idea of musical form as generated by an extramusical idea or expressive narrative is essentially Romantic (though not without precedent), and Beethoven bears much of the responsibility for its ascendance. You can bet that the opening movement of the "Eroica" was not readily grasped as a form by its early hearers, and they were right in sensing a difference between its dramatic narrativity, which would have sounded to them like an excess of fancy, and the tight, balanced, easily perceptible Classical structures of Haydn. Wagner reasonably (from his Romantic perspective) saw this radical aspect of Beethoven - his sense of musical drama and the theoretically limitless expansion of form it suggested - as pointing toward actual drama on the stage, to be conveyed through music of symphonic scope.
It isn't quite right to say that the logic of Wagner's operatic music takes a backseat to narrative, since dramatic narrative, in many instances, provides the logic: dramatic expression is what the music is,
and it makes no sense to look for "purely musical" justification for what is an essentially a dramatic idea. Wagner, however, had an uncanny skill at developing his motivic material and integrating it with carefully plotted key relationships to create a psychological progression, an arc of feeling, a structure with direction and coherence meant to be felt rather than grasped intellectually. It's been remarked that his music, by subjugating form to expression, breaks down the aesthetic distance, the mental "proscenium," which mediated between the composer's art and the listener's perception, and which had characterized the experience of music up until then. And yet, closer examination reveals a surprising quantity of traditionally balanced musical forms embedded in his huge structures, forms which are simply prevented from imposing themselves on our intellects by means of clever interlockings and harmonic deceptions.
I'll also remark that Berlioz's idee fixe
barely encroaches on the musical and dramatic elaboration of the Wagnerian leitmotiv.
Wagner disliked the term "leitmotiv," preferring the term grundthema
(roughly and clumsily, "theme which is the basis") which better describes the musical function of his motifs. His practice of thematic transformation, his ability to get seemingly limitless mileage out of simple materials, has no more potent ancestor than Beethoven's fifth symphony.
Wagner was aware of the dangers posed by the attempt to apply some of his dramatic effects to abstract instrumental music, noting that "for the symphony one proceeds very differently," and he mused in a letter to Liszt about a concept of symphonic writing based on thematic metamorphosis. That sounds a bit like Sibelius, but we can see the principle at work in some of his orchestral passages. Too bad he didn't live long enough to get around to those symphonies.