While I was going through the forum at TV.com, I stumbled over a discussion about the worst cartoons from Nickelodeon, a TV-station for kids (even though I personally watch some programs on the German branch as regularly as I can, too). One of the cartoons mentioned there quite often was "All Grown Up", which is a spin-off from the cartoon-series "Rugrats".
"Rugrats" was aired first about ten years ago in Germany - when the last incarnation of Nickelodeon was on air here - and it surely was an unusual program, too. It centred around four babies (Tommy, Chucky and the twins Phil and Lil) and a three-year old (Angelica, Tommy's cousin). The four babies were the stars, going through adventures which quite often were a combination of their abilities (Tommy was masterful with his little toy screw driver) and their imagination. Angelica on the other hand was some sort of Nemesis for them, usually cheating on them to gain something (more cookies, more admiration or other stuff). The second season featured Dil, Tommy's younger brother, and Kimi, Chucky's adopted sister, and had Susie (the same age as Angelica and her friend, but much nicer) appear more regularly.
"Rugrats", though unusual in style, was an extremely successful TV-series, successful enough to even sprout of a movie a couple of years ago. This probably was the reason why Nickelodeon decided to create the spin-off "All Grown Up" in which Tommy and his gang are about 11, Susie and Angelica are about 14 and Dil is about 10. There are some connections between the two series. For example the "Java-Lava"-café which Chucky's father and the twin's mother opened in the second season of "Rugrats" still exists in the spin-off.
Unfortunately "All Grown Up" is regular in everything except style (which is based on the "Rugrats"-design and still not common). It's in many ways a run-off-the-mill junior high school series with the usual problems and stories. It could be exchanged with other Nick-programs easily, for example with "As told by Ginger" (which is even a bit more innovative) or some of the real-live series like "Unfabulous" or "Zoey 101".
As such series go, it's not bad, but compared to the predecessor "Rugrats", which really was innovative and interesting to watch, it's just not up to par. On the whole it would have been advisable for Nickelodeon to either put some more energy in the development of the series or not create a spin-off of such a highly-successful (because highly unusual) series.
The characters - which were already mostly developed in "Rugrats", except for Dil who was just a little infant then, even compared to the others - surely would have allowed for a better and more innovative series. They aren't that usual (even though I still wonder why Tommy has turned from the creative inventor he was as a baby into a wannabe producer), especially Dil, and they would have made an interesting group going through a more unusual adolescence. Just using the characters and coupling them with the usual junior high school stories doesn't do them justice.
Those probably are the reasons why most people seem to see "All Grown Up" as one of the worst cartoons. I can understand them and I mostly agree with them, but I see that it's not the series as a such that's so bad, it's the fact that Nickelodeon has taken the basics of a very unusual series and turned them into a mediocre one.