Re: Pratchett Essentials
I don't dislike the Discworld series, but if we're going for top 5 I'd actually suggest the Johnny Maxwell trilogy myself. I know it's supposed to be aimed at younger readers, but it's less blatently fantastic, though still fantasy, and I found that made it easier to care about what happened to the characters, - the Discworld stuff is too mad-cap for me to put my heart into.
This trology has a more consistent tone and POV, and more compassion and heart than the Discworld ones, while still being funny.
Just my opinion.
Or if you specifically wanted Discworld, then: Soul Music, Hogfather, Reaper Man, Masquerade and Men At Arms.