I found this story deeply disappointing in the end, though I will admit that it was quite a ride getting there. Essentially, my problem with this story was the title. I spent half a year in Prague in high school, and while Prague is definitely a modern city, it is a city with a distinct style. There was nothing characteristically "Prague" about this story, just a lot of Praguian (Parugian?) name-dropping. You could have called this story "The Song of New York" or "The Song of Chicago" or "The Song of Vienna" or "The Song of Hell, MI" and it wouldn't have changed a thing, except for stripping off the veneer of European sophistication (which is, I suspect, why Prague was included in the first place).
And if something has no purpose in a story it's a waste of words.
I agree with 'Cat that I could have done without Concluding Explication, or at least without quite as exhaustive an explanation. In fact, I was hoping that the sisters would deem his failure a reason not to tell him anything and leave him to stew in his questions. Forever.
[Actually, I was hoping that for failing to protect the sisters from Toothy McBloodpaws he'd become a Toothy himself, but that just shows how my mind works]
That said, I found a lot of the story very appealing. The idea that the world we all know and love is quite that tenuous, held together by a secret society of lullaby singers who arrange to keep the song sung in cities everywhere so that the sleeper will not awaken is brilliantly creepy. The sleeper's chaos manifesting as complexity of form (building, living things) collapsing into rigid and dead, but geometrically perfect forms was neat, too.
And I also dug the unlikely hero angle. You never know what's in you until suddenly you have to find out.
As the Magic card says: every moment has its own savior.