I 'd have to say it is one of the best "on-going story" in the manga & anime world. Ten years and it's still going strong. For those of you who have studied mythology and have been following Naruto since the beginning, you will recognize the Naruto story as a classical 3 part Act. The early or first Act (Naruto) laid the foundation of the story through a fun and almost innocent story telling. This is the time you learn about and identify with the characters.
The second Act (Naruto Shippuden) is about the trials, tribulations and conflict between the characters and how they learn to deal with them. In mythological terms, this is the part where the metaphor of "killing the father" takes place. In other words, the main characters will surpass their teachers, mentors, parents and address their conflicts on their own.
I strongly suspect there will be a third Act and it will be a story about resolution and the "coming home" storyline ... or the fulfillment of the prophecy.
Bottom-line, to get the full benefit of the story, you really should follow both the manga and the anime - the manga is a very focused story with very little "excess fluff" to distract you from the story. The anime on the other hand is like a 3-D movie, it adds fluff to the story, but this fluff helps refine the depth of the characters and fills in tidbits of information the manga doesn't, or is incapable of doing.