This was real. This world of monsters and impossibilities. It felt hard, dangerous, solid. Everything else, the soft and safe things she'd grown up with in the worldsphere, suddenly seemed as vague as holograms or old memories. And !X… 
!X was the realest thing of all.
This is one of the best novels featuring Bernice Summerfield, in league with even Love and War. Though on the surface, this seems to be a simple story of an expedition into an Inner World but Miles give a lot of postmodernist depth and breadth to the tale. It is by turns comedic, haunting, and fascinating. It has some of the best-written characters and a fascinating plot filled with thought-provoking twists. The worlds of Tyler's Folly is one of the most memorable within Benny's adventures if not within the DW canon. This novel also serves as a good introduction to the People to those who haven't read Aaronovitch's The Also People (which I have not yet).
In conclusion, a very good introduction to Benny's solo adventures and an extremely good novel in general.