Dan Castellaneta voices a character called Grandpa in The Simpsons. Dan Castellaneta voices a character called Grandpa in Hey Arnold! The Movie. Here endeth all comparisons between the two.
The basic 2-D animation of this Nickelodeon TV channel spin-off looks embarrassingly past-tense on the big screen, while the script - despite a sharp pace and the odd character quirk - isn't likely to hold an eight year-old's attention, far less the poor parent who drew the short straw.
Maybe we should blame those Pokemon movies. If they hadn't done so well (early on) at the box office, then we'd have been spared a string of cheap TV cartoon cash-ins with no cinematic value.