Aion
Time-Traveller
You only seemed appealing at the very beginning; a typical type of trash.
I'm sure most Narutards could tell you who said the above.
Ironically, the very same dialogue Studio Pierrot came up with to insert more feeling into the scene does fit Naruto (the series) live a glove. It's a better fit for the manga since, unlike the anime, it wasn't split in two but it does also apply to the Naruto anime if you think of both series as one.
Bleach is another series that the quote describes pretty well due to both the anime and manga going down south after a great start to the story. Also, Kenshin (anime) is yet another shounen the quote applies to as a result of the filler hell that killed it.
Code Geass also springs to mind, although with CG it's more a case of the story going downhill since S1 (the 11/10 start) and S2 (the poor continuation) split the good and bad in two, much like with Naruto anime.
The Death Note manga is yet another title the quote fits, the manga author seemingly not knowing what to do after IT occurred. Thankfully, Madhouse were awesome enough to be able to paint over the cracks and keep DN amazing until the end.
My final mention needs to go to TTGL; a series that started very well and ended horribly, the events of the last section of the story being stupid to the point of retardation. I've semi-hated the series ever since watching it due to its 10-13 fans of it ignoring all faults and rating it 10/10.