Discworld fans tend to have less regard for the first books, but they're not bad; it's just that they're a different kind of satire: primarily parodies of high fantasy literature, rather than satires on the real world as Pratchett saw it (though there was already a bit of that). The focus changed.

The Discworld universe is divided into sub-series focused on different characters. You don't have to read the whole series in sequence. I think I might have a harder time reading the Vimes books now, just because I have a different attitude toward cops and police procedurals than I did when I read them. If Guards! Guards! didn't appeal (as to Patrick above), I might recommend reading more of the books about the witches or about Death.