Although Pixy compared PuPiPo to Haibane Renmei, what he really meant is the progression of the escalation in the story. Watching it, I went like so:

01: A little girl can see ghosts, how cute
04: An adventure in the otherworld, nice
09: Future adults, this is getting interesting
13: Now they are kicking ass
15: HOLY CRAP WHAT IS THIS?!

I don't know about you, but I didn't see that coming.

Unfortunately, the anime is spoilable, so I cannot relate the details... But the episodes are only 4 minutes, so we're talking about 2 normal episodes worth of the story here. Anyone could watch for themselves. And they probably should.

Liked: Oh yes
Rewatch: Not impossible.

UPDATE: Don calls PuPiPo "funny and poignant".