The Discworld books, while so far being very readable in chronological order, are also broken up into loose 'themes' depending on the characters involved. Wyrd Sisters, Pratchett's next novel after Sourcery, is also the second in the 'Witches' mini-series. This, in a sense, makes it the sequel to the two books I found rather disappointing, so I was a little apprehensive about starting it, lest it be more of the same. As it turns out, I need not have worried, as Wyrd Sisters is anything but boring.
Equal Rites, the first book in the Witches series, started out well with some strong characters and a welcome change of tone from the previous couple of novels. Unfortunately, it seemed to quickly revert back to form, and I felt that very few of the interesting new ideas Pratchett had were properly realised; we were given a brief glimpse into a very different aspect of the Discworld, only for the action to once again return to the same parts of Ankh-Morpork we were already familiar with.
Wyrd Sisters, in contrast to this, really feels like a different setting, and is all the better for it. The wizards of the Unseen University do, inevitably, make a cameo appearance, but it is a brief one and most of the action is set in the Ramtop mountains and centres around a different, and very interesting, cast of characters. There's a dysfunctional coven, a scheming duke afraid of what the trees are saying about him, an intelligent (and rather depressed) fool, and a royal prince being raised amongst a wandering theatre troupe. The whole story is told from Prachett's irreverent viewpoint but, no matter how ridiculous they might at first seem, every character is human enough to feel like someone you've met; or at least the larger than life version that inhabits all the best anecdotes.
I am reliably informed that the plot is loosely-based on Shakespeare's Macbeth (I've never got on with the bard and consider his works to be rather overrated), but, if so, Pratchett has altered things enough to make it his own. I won't spoil the plot too much, but it's the first really coherent one in the Discworld series and the story if all the stronger for it.
The best book in the Discworld series so far. Full of brooding atmosphere and insane humour. Highly, highly recommended.