Cute...not as funny as other Terry Pratchett books. I haven't read the other first two books in the series, but they didn't seems to play to largely into this one's plot. Children's book, definitely more geared towards girls.
As with most of Pratchett's books, I found 'Wintersmith' to be extremely entertaining, but not exceptional. Unlike many of the Discworld books, this novel will definitely be helped along if you've read some of the previous books in the series that deal with the same characters (The Wee Free Men, A Hat Full of Sky).
I've read the first, but not the second.
The story deals with the teenage apprentice witch, Tiffany Aching, who is helped/hindered by her friends the Nac Mac Feegles (blue, Scottish-flavored 'Pictsies'), when, due to an ill-advised dance, the titular elemental spirit of Winter falls in love with her - with less than salutary effects on the climate.
Engaging characters and witty writing, but a fairly typical coming-of-age-type story.