Broken Sword games are definitely worth it. The first one, The Shadow of the Templars/Circle of Blood (depending on where you live) is by far the best, but the others aren't bad either.
If I were you, Achrono, I'd start from the beginning of the series and play them in the chronological order, but I guess they can be played in any order you like. Some people hate The Sleeping Dragon, but I really enjoyed it.
What do people think of the fourth one? To me, it was a pretty bad disappointment. The godawful ending is in a league of it's own, but I also felt that the plot could have been told a lot better. Of the minor characters, only Mark touched me in anyway. It felt like most of the cast had no flesh on their bones, and this definitely goes for Anna Maria. For a character that the player was supposed to care about, she was horribly hollow. And I can't get over the disappointment of them not putting André into the game (apart from the small reference).