I just finished this surprisingly wonderful game, Apart from a few minor disturbances (long scene loading times, and a very annoying delays when talking to a certain sculpture and varying voice-over volumes).
I do believe this is the first time I enjoyed a comic adventure game for being fit to ADULTS.
Even compared to LucasArts (Including GRIM), the dialog and story here, although being comic, is very witty and mature.
The amount of dialog really puts The Longest Journey to shame. It is endless. But - Never boring.
I played this game over a few weeks, 1-2 hours a time, and I guess playing it straight would have been a bit tedious.
Graphics are nice and so are the voice-overs, but you should play this one for the story and the dialogs.
This game has restored my faith in comic games (which I got fed up with after playing Curse of Monkey Island and Grim Fandango in a row).
Another advice : This is a VERY long game, and this is so mainly because of the amount of dialog and the fact that you need to ask a lot of people about a lot of things. If you get stuck, and you feel a bit let-down by knowing that there are 100 things you need to ask 10 people about now, and you don't feel like it, either stop playing and return in a few days, or use a hint. This will not spoil this game and it will still be long. Just don't overdo it, and try to make sure you don't use a hint to solve a puzzle (this can be done by only asking people, and not looking at a w/t).
I have played the previous 2 (unconnected) games, and didn't feel this way about them. I thought they did Pratchet's work injustice and were a bit childish.
This one isn't.
So - Just to be clear :
PLAY THIS GAME