The thing I want to say about Pratchett's Death is that he achieves something philosophically serious under the cover of comedy. Death is not afraid of Death. He is curious about it. He finds human existence bewildering and moving. He is, of all the characters in the Discworld, the most sincere.

In Reaper Man, Death is fired. He goes to live among mortals and discovers what it means to do things for their own sake — to harvest wheat because the harvest is worth doing, not because it's a function he performs. This is an argument about meaning that holds up outside of the comedy context.

Pratchett was diagnosed with early-onset Alzheimer's in 2007 and wrote several more Discworld novels before he could no longer do so. Whether or not you find the Death-centric novels funny — and I think they are — they are clearly the work of someone who had thought carefully about mortality and found something worth saying.