I read this recently.
I think it demonstrated his future brilliance, particularly around evocative description. In parts it's astonishing and reveals the linkage to Gormenghast, especially with the roof top descriptions.
But at times it was awfully juvenile, so much so that I almost put it down. The sixth form pseudo NME adoration of drum and bass, (ooh it's soo important), infuriated me and completely threw me out of the story. It read like an eloquent teen's fanzine.
I struggled with Saul's blase acceptance of his new ratty life. As for his friends, they couldn't die quickly enough for me.
I liked the King Rat Saul encounters and could have done with more of that. But I struggled with the motivation of the Piper, what was his aim, why? The revenge explanation didn't cut it for me.
So brilliant in parts all breathy wide eyed enthusiasm in others.