Redwall would be the place to start. It’s not first chronologically but it was the first written. Actually, there are very few books that need to be read in a certain order. For instance, I wouldn’t read The Bellmaker until after reading Mariel of Redwall since The Bellmaker comes immediately after Mariel of Redwall chronologically AND includes the same characters.
The series covers a huge span of time, from long before the Abbey is built until long after it has been built so most of it can be read out of order without too much trouble. However, I would still read Redwall first.
I can’t say you’d like his books because you’re a Pratchett fan. My boyfriend and I happen to be fans of both but the two don’t necessarily go together. I find his books to be better than Pratchett’s (but only slightly) simply because of the depth of the detail.
The series is about animals. Some animals live in Redwall Abbey and some live at Salamandastron. They are good animals and the main groups in the books. There are always bad groups of animals (Vermin - always) and they come from all over. There are battles and feasts and epic quests and a whole lot of humor. He is incredibly descriptive because the first book was a story he told to blind children. The books are also filled with songs and poems.
I love to read them but even more I love to listen to them. Brian Jacques narrated them and he has a wonderful voice. Each audiobook has a large cast though and the variety of voices is so cool. I love to listen to them in bed, with my eyes closed, visualizing all the wonderful details. It’s like seeing a play almost.
MunkaMike Have you seen the Redwall Cookbook? I bought it for my boyfriend and his mother promptly stole it. The Deeper 'n Ever Turnip 'n Tater Beetroot Pie has replaced all veggie dishes at every holiday meal. I was actually going to suggest The Long Patrol as the second book to read. I love that book. Those two and Salamandastron are my top 3 favorites.