I'm playing with the idea of a dream sequence as a prologue to a future comic, and I feel the same trepidation as you do. On one hand, it is so overdone, where fantasy prologues are concerned. On the other hand, it's so effective for conveying lore and history, along with setting up expectations for an eventual shift to a darker tone with deeper fantastical elements. (Otherwise, I worry that the beginning of the story, being rather light, will attract an audience who won't be keen about the story becoming more heart-wrenching later on.)
I think, if the idea truly works for your story, go for it. Write it in a riveting enough way, and most readers aren't likely to care that it's considered overdone.