I loved Nation - despite it being a non-discworld novel. As with many themes in the disc-world Sir Terry managed to make some real sociological points without upsetting some group because they couldn't see past the setting to the message.
I'm over 50 and teared up a couple of times when reading it for the first time, and always feel moved every time I read it. To be able to cover such a moving story and still have humour in it - well, that is what makes a Prachette novel so good.
I remember reading Joseph Conrad and HATING it, the story was so black, depressing and horrible, but the writting was so good - I could feel the characters in my head - I felt for all the charcters in Nation, but the 3 gifts of Pandora were there too - maybe that's why Sir Terry is fun to read - he still has hope etc...