All three of these books are great.
I found these books almost as captivating as Heroes of the Valley. Don't get me wrong, the story line is completely different, but it still follows a young man as he grows from a child into an adult. Although it's a bit more fantastic than your average child-to-adult experience, it's certainly got all kinds of elements that you can relate to! It's also got demons. How can a book about demons possibly be bad?!?
Steampunk sorcery type stuff
Anything that is related to wizards
Demon type armies or characters
Traditional monsters such as gargoyles, zombies, and skeletons.
On the surface this book resembles a bit of Harry Potter; the kid doesn't have his parents, he learns how to be a magician, etc. etc. Unlike Harry Potter, it somewhat represents a more realistic scenario regarding how the world would look if there were actually wizards in the world. Furthermore, magic isn't free, and a price has to be paid...
Enter the demons. The story is basically told by the young man and the demon Bartimaeus. The demon's character is simply fantastic, and his constant references to his vast past really adds depth to the already delightful character. This allows the listener to be able to relate to the old and wise demon as well as the young and naive kids who's growing up.
Naturally, there's a hint of romance as well, just enough to keep things interesting. Furthermore, it's the link to outsiders that really makes the boy's life that much more compelling. Over all, it was a trilogy that I would highly recommend.
It's worth noting as well here that there was a fourth book about Bartimaeus, and I chose not to include it here since in all honesty, it didn't really fit with the trilogy. I didn't find it nearly as good either, but hey, listen to it yourself and you be the judge ;)
Over all, a strong storyline throughout, great, compelling characters, and a world that is highly believable yet still entertaining. It is definitely a good one to listen to while painting.