I really dislike In The Zone, and think it's her most overrated album. IT had so much
filler, and apart from the singles (Everytime & Toxic ,and I'm being kind including Me Against The Music), Breathe On Me and Touch Of My Hand...it's the album I return the least too.
I appreciate ITZ, for what she delivered aesthetically from that album (i.e. the videos, performances, and her getting more involved) but outside of that I do not use. Showdown, Early Mornin, Outrageous, Brave New Girl (

) and Shadow are nowhere to be found on my itunes
Pure enjoyment wise, without taking into consideration of what actually happened during each era:
Blackout >> Femme Fatale > Oops! I Did It Again > Britney > In The Zone > Circus > Baby...One More Time