OH MY GOSH WE'RE TALKING ABOUT TERRY PRATCHETT?!?!?
*deep breath*
I just re-read Thief of Time which is one of my favorites, and which I haven't read for years. After all this time, I still want to be Susan Sto-Helit. I haven't read Reaper Man in a while either (though I read it for the first time much later than many of his books, since my brothers and I sort of collected them as we came across them and read everything out of order) and your Tumblr posts have been making me want to read it again, Yuu.
I did read The Shepherd's Crown. The foreword will explain this, but it's a little less polished than his other books - for the simple reason that he wasn't done polishing it yet. I don't want to spoil anything, so all I'll say is that I enjoyed it (in a sad kind of way) and there are a lot of elements around the theme of growing up, growing old, and dying. So make sure you're in the mood for that kind of thing when you get around to it.