I guess it all depends upon your own opinion of each series, and on your defintion of "true to the series."
I personally thought Seasons 8/9 were better than I expected them to be, and I throughly enjoyed them. Considering that I haven't read that much of Charmed Season 9, I can't really compare the two of them, and I'm not sure that people should. They are each their own series, and as such, have a different 'feeling' from each other.