Through professional analysis, it is realized that Naruto is put together rather haphazardly. The storyline is somewhat bland and filled to the brim with cliches. The story's pacing, at least in the anime, is HORRIBLE. There are times when the action is moving at a good clip, but more often than not, the episode is spent watching the characters stand around gasping in horror/having myriad flashbacks, without anything of particular interest actually transgressing. The artwork is not the greatest, and the animation is only decent. The english voice dub sucks total balls, as well. So why is it popular?
The obvious reason is that youth these days are becoming mindless nincompoops from sources such as Television itself, the Internet/Computers (even this forum), and a variety of other activities which lack schedule space for physical or real mental exercise. As a result, kids tend to demand cliched media when it comes to anime, and in these regards, Naruto satisfies. Naruto doesn't take much intellect to enjoy, and thus is a good show for modern youth, 60 some percent of whom are also overweight.
But I think the underlying reason of Naruto's enjoyability, as well as the enjoyability of most forms of media, is atmosphere. The atmosphere generated by Naruto is just so agreeable, a feeling of complacency and carefreeness. Atmosphere is typically generated by the Music and the style of drawing when it comes to a show/video game, more so than the premises. If Naruto had been drawn differently, or the Music was different, I don't think it would be anywhere near as popular.