To back up my orchestral music is easy to impress with, consider the example of Hector Berlioz, a name that would never be praised if it wasn't for his orchestral innovations. Berlioz's music was almost completely vacuous, and had only smatterings of moments of quality. In fact, Berlioz is one of the only well known composers I'd list below Mozart, and we've had the Mozart conversation before [flashes the secret handshake].
I'm actually more irritated by the idea that Mozart is so low in esteem as to only allow one or two composers to be placed beneath him, but this is just another of those "To each his own" sorts of things.
But as for Berlioz, this opinion is hardly uncommon, I must admit. I'm a long-confirmed Berlioz obsessive (look for my series of posts, linked in the sidebar, in honor of his bicentenary), but I've also seen first-hand how many people who love classical music just don't get Berlioz, for whatever reason. I have a friend with whom I occasionally share music; I send him stuff and he sends me stuff in return (actually, he sends me a lot more stuff than I send him because he's twenty years older than me and it's thus a major challenge finding stuff that he hasn't heard already). Some years ago I sent him some Berlioz -- Romeo et Juliet, if I recall correctly -- and his response was a very polite "Meh". And this I've heard from many others. But I've also heard from people who, like me, utterly adore Berlioz. (To this day it irritates me that at the Impressions de France film at Epcot Center's World Showcase, the film -- a series of stunning images of France set to French classical music -- includes not a single note of Berlioz.)
It's generally been my experience that Berlioz gets two responses: "Meh", and "Oh my God, I've just had an orgasm." (Rachmaninov is in a similar boat, although he gets more of a range of reactions.) This is not new, either. Here is Harold Schonberg, writing in his grand old book The Lives of the Great Composers:
Perhaps Berlioz will always remain the object of veneration by a strong and articulate minority. He could not speak to Everyman. But there is not one piece of his that lacks its incandescent moments. And then Berlioz is seen plain, his eagle beak defiantly thrust at the heavens, glorifying in a kind of tonal magnificence and an ideal of self-expression that make the concept of Romanticism very clear.
And, more recently, David Dubal expresses the same sentiment in his Essential Canon of Classical Music:
Still, it took most of the twentieth century to place Berlioz's art in perspective. He has always irked many people. He refuses to fit into a convenient niche. His works as a whole are not graceful; they do not have the kind of melodies that stick in the mind. His harmonies can sound primitive, and his content empty. But for those who are temperamentally attuned to him, he is shattering. He has a subtlety of construction that goes beyond technique, and his orchestrations have proved to be models for generations to come.
Whenever I hear any of Berlioz's music, I think of the poet Heine's statement: "He is an immense nightingale, a lark as great as an eagle...the music causes me to dream of fabulous empires filled with fabulous sins."
And there you have it.
(Oh, and the Greatest Composer of All Time? The best historical case can probably be made for Johann Sebastian Bach, but even then, I still believe that the sentence "Bach was the greatest composer" can never be a true statement in the same sense that "Jupiter is the largest planet in our Solar System" can.)