Re "The Hunger Games" trilogy - one could argue that the ending was a bit of a downer. (I don't want to do any spoiling here.) I personally thought that it was well within the context of the stories. Katniss et al have been through a whole lot. They're not going to come out of everything unscarred.
I'm in agreement with Labby - I thought it was an excellent series. It's certainly one that left me thinking for a long time afterward.
