I have really enjoyed this as an audio-book only series. The voice acting and music add a ton to the experience, IMO. It also helps keep the characters straight, as the actors have distinct voices. I have played plenty of RPGs, so the various references throughout have been fun.
To the question earlier:
Lucia Mar is sometimes controlled by the children in her head. They still don't know how it works, but it has something to do with the gods. She is probably the most important side character to the team as they are convinced that her death will lead to the death of hundreds of thousands of children. Katia (from the earlier books) got pregnant specifically to get transported to the kinder facility and avoid being killed by the same quest that required Princess Donut to kill all the nagas. Jurgen's wife, Heidi, is also there and it was revealed in the most recent book that she was somehow able to talk to him but has stopped. I assume this plot line will not be cleared up until the last book.
Li Na has gone somewhat psychotic since the death of her brother (she is part of an original 3 man Asian group). She was sent through the cleaner bot to keep her from killing the other crawlers in the races.