You either like it or you hate it. I happen to like (most of) it quite a lot. I think Thud!, Snuff and Steam do a very good job of digging into social/racial issues. I think Steam and Jingo do a good job of skewering how easily we write off other cultures. Making Money apparently does a better job of explaining modern economics and the Fed better than most text books.
While the series as a whole does make reference to earlier books on occasion, you can honestly pick up darn near any book and enjoy it. Again, I would strongly recommend Thud! as a good one to pick up. If you don't like that, don't bother. If you do, any of the others I mention above will work for you.