Listening to Prokofiev's 2nd Symphony, it struck me that this is the sort of brilliant, but eccentric and ultimately unsuccessful piece that only a composer of genius could write. Isolated parts make a strong impression, but as a whole it just doesn't hold together.
I'm tempted to think that Schoenberg's serial technique is the kind of misstep only a genius could make. While I like certain products of it (like the Op. 31 Variations), on the whole I think he made a wrong turn when he went this way.
My early impression of Bach's Musical Offering is that it too could fall into this "dud of genius" category. I need to get to know it better, though.
Your candidates for "duds of genius"?