Having just seen A Letter to Momo, Wolf Children and Rainbow Fireflies at the Waterloo Festival for Animated Cinema last weekend (November 15-18) I really enjoyed all three but came out thinking that the story in Momo was the weakest of the three though the ending kind of saved it and the animation was really, really well done. I found the story for Rainbow Fireflies to be the most touching and it had some simply amazing animated sequences as well.
It is interesting as all three seem to have a nostalgia for the countryside, nature and the spirit world. The characters are getting away from cities or being kicked out of the countryside against their will. The connection to nature and the supernatural has been lost in the modern world. You must make a choice, you can't have both a connection with nature and spirits and be modernized without losing something.
Too bad I haven't seen Poppy Hill yet.