Zabusa Arc - Great, watched it back then
Chuunin Exam - Mostly good, had its share of good and bad
Rescue Sasuke - Declining, although a few badass moments to make up for it
-- TIMESKIP --
Rescue Gaara - Declining further. Anime version sucked shit due to DBZ-like pacing. Manga wasn't much better, but it had its moments
Sai Arc - This is where the fail sets in. Sai sucked as a character, the plot was stupid, and Naruto degraded into a slobbering Sasuke-fangirl. Only highpoint being K4 Naruto vs. Orochimaru.
Everything after the Sai arc is just the series getting progressively worse. People keep up with it in hopes that it will get better, but hopes are often dashed. Manga might as well be called "Sasuke" now.