Hi, I've read all of these they are great. Earlier novels are not available on kindle though, I would suggest reserving from the library if this is a facility open to you OR buying from Ebay clicky link
I accidentally stumbed on these (first one I read was 7 up when it was on a 3 for 2 deal in waterstones many years ago) and I've read them all.
I always get the new ones from the library though despite being an avid kindle reader as they are quite expensive (later ones are available on the kindle).
Yes totally agree earlier ones are better, I always reserve the new ones as I want to know what happens next!! The film was pretty awful (One for the Money) but Janet Evanovich sold the rights years and years before the the books were popular.