Hi
Try it!
Pratchett has a dry humour, uses (I think) clever allusions to history and science, has some interesting twists on common myth and belief (check out: Lords and Ladies) and just really interesting plot lines.
I am a big fan of Pratchett. Although I agree it can be a bit of a mixed bag at times.
I am a big fan of the Guards series (Guards, Guards; Men at Arms; Jingo; Thud; Night Watch - I have probably forgotten one or two - sorry).
Color of Magic, Light Fantastic are quite different, from the later stuff (as I guess you would expect as he gets to grips with his characters and the readers get to know them better). What turned it for me was: Mort (the first in the Death series) - my copy is ragged now and probably time for a Kindle edition (which you can buy in Australia)
I like Pratchett's dry humour, clever allusions to history and science and just really interesting plot lines.
I like the Witches series too (check out Wyrd Sisters - the Discworld take on Macbeth...).
You can also look at Good Omens (jointly written by Pratchett and Neil Gaiman).