It has that same comic humour that Discworld fans have grown accustomed to. It's hilarious, but that's not the best bit. Because it's a game, it's important that it be substantial, interesting and fun.
As you solve the problems in the game, you are rewarded with humour and fun new twists, (as well as new problems, of course). The problems and solutions trickle together as you work your way through the game, and you get to know the characters that you've no doubt read about, (even if you haven't, you'll be intrigued,) like Casanova the Dwarf and the Wizards and their super brain machine.
Discworld 2 has much better playability than the first one. The controls are both easy to learn (and to use) and feel very natural.
The world is silly, but it works. Very much the Terry Pratchett way and it just makes sense that Eric Idle narrates.