Wow. I felt this ties in nicely to the original story. The main differences is that I felt Oz is a bit more fantastical here (flaming toast, prebuttered, cooked corn still on the stalks, etc) and that Dorothy seems a bit conceited and selfish even from the beginning. The setting when she was in Kansas did feel a bit modern though. 
 Danielle Paige does a great job with references from the original book. She bases is more on the books than the movies since the ending is fairly different. Going from the original story to this is a fairly smooth transaction. 
 The questioning of Ozma and missing Glinda was a great idea and the way it plays out is interesting. You really get a glimpse of how Dorothy changes from the sweet girl who first journeyed the Yellow Brick Road to go home, the the wretched brat she is in Dorothy Must Die. Eager to read the next step in the prequel series!