That would be my one sentence review of this movie and the TV show that it is based on, but I'll go more in depth. This movie is likely to weird out and drive away anyone who's not a fan or a casual viewer of the series. But if you haven't seen anything relating to Keroro Gunso, the plot is not very hard to figure out. The movie assumes that you already know who the characters are, so you may be left in the dark in that respect, but it's about a frog-like alien and his companions saving earth, so you shouldn't be in too much trouble. As a film version of Keroro Gunso, it probably delivers for fans, since it has all of the main characters in it and even a few minor ones. The humor during the film is a bizarre combination of cutesy little kids jokes, pop culture references to Anime and well known films, and occasional stream of dark, apocalyptic creepiness. The deadly serious tone that filled much of it confused me, sort of like if The Simpsons Movie was about Homer dying of cancer. But the grim tone of the x- marks as well as the many forms of the creature Kiruru (filling in the role of boring villain created solely for film version of TV show) inspire some "aw, cool" moments. The voice work is serviceable. Standouts are Takehito Koyasu, who manages to carry the same detached sleaziness that made his character Kururu stand out as the most interesting in the TV show, and Haruna Ikezawa as Momoka, which isn't really surprising for those who've seen the series. As for Gunso himself, Kumiko Watanabe screams and wildly acts, which promises to be a fun portrayal, but as in the TV series, there is some sort of passive blandness to our main character, probably due to his 3-note personality. So, the movie manages to translate the series to the silver screen fairly unchanged. Like the show it is diverting and fun, but goes by so fast and leaves such little impression it's hard to care. Watch it with beer and friends and it can pass the time (assuming you and your friends are alcoholic otakus).
EDIT(2008): Wow, this review is horrible. I did it when I was, like, up at 3:00 in the morning, but that doesn't make it any more tolerable. I still stand by most of these opinions, but JEEZE, my writing style was god-awful. Turn away, folks.
