If "Eric" were a food, it'd be a hot dog. It feels like Pratchett took random bits of humor that weren't good enough to make it in other books, and mushed them all together. Eric is the lips and assholes of Pratchett's storytelling.

Eric seems to exist soley to resolve the cliffhanger ending of Sourcery, and it does so with a moderately amusing Deus Ex Machina. The rest of the book is more like a Family Guy episode than a coherent novel.