Good-it's technically not a symphony (actually a symphonic poem which is somewhat related to a symphony, but not this case).
Now to unstart a war I could've instigated with that comment, Scriabin referred to it as his 4th symphony at least twice in private, but generally referred to it as a symphonic poem. The consensus is that it is so vastly unsuited to the descriptor/title 'symphony', that it's better to acknowledge it as a symphonic poem. It's a very fine line in some cases. Sibelius' 7th Symphony is about the same length as The Poem of Ecstasy, but because of the way it handles thematic material, that is a symphony.
The Poem of Ecstasy handles its 3 major themes (the first signifying the human spirit, violin theme for human love, and trumpet call being the will to aspire) in a free-from fashion. The structure is meant more to tell a story without using traditional methods (e.g. sonata-allegro or ABA) than fit into a true form. There's till bits and pieces of traditional structure, but they don't matter.
Sometimes, with careful planning, a piece that perfectly adheres to a form can tell a story, albeit somewhat limited to simple gestures and events. The removal of exact structuring was a major facet of Romanticism (it was a progressive progress, at first it was little alterations, later it gt to be lobbing off limbs left and right). Without it, stories can actually be revealed to the listener in a much more natural way, letting the listener to come to the implied meaning much faster. All different degrees of emotion could be expressed. Of course, when there was no official program, meaning could still be found. All sorts of meanings.
The opposite of that would be absolute music. Music that exists [originally] only to be music. There's still meaning to it for some people, but not necessarily to the composer [past the aesthetic level].
Now, for more music. One of the biggest "fuck all of you"s in modern (1600s-now) western music history. It transcends all previously accepted practices. It throws them out the window in favor of musical expression. Parallelism, endless layering of 5ths, modulation without transition, chords being moved freely around as block units, calling for lack of nuance (notes completely as themselves), clusters, lacks of thematic development (actually no themes, only motives), with fragmented motives being the basis for all, unaccompanied nths, you name it (except atonality, this work is mostly tonal). It is more-or-less Debussy's abandonment of traditional thinking, and one of his most defining works.
