Sir Pratchett has been a major influence in my life and my husband's, and our love for his works is one of the things that brought the two of us together, and influences both of our writing styles. No one, NO ONE could set up a joke like Sir Terry!
We were lucky enough to attend the North American Discworld Convention when it came to Phoenix, rather than going to what turned out to be the final Gargoyles Gathering. As Gargs fans, we were kicking ourselves about it, but given that this was our once chance to see Sir Terry in person before Alzheimer's took him, in retrospect, we feel like we made the better choice to see him.
For those who wish to start reading the series, I'd say, don't let the first book discourage you; he hadn't hit his stride yet at that point. I started with the second book in the series (Light Fantastic) by accident, and was hooked... I don't know if I would have been had I started with Color of Magic. "Eric" is generally one to give a miss.
My personal favorites are Soul Music, Going Postal, The Hogfather, and Good Omens (with co-author, Neil Gaiman).
And if you have an hour:
The Importance of Being Amazed about Absolutely Everything
If you don't have an hour, tl/dw,