Though I cannot deny this anime is full of silly moments and lots of fanservice, making it one that it is seemingly more or less geared toward true anime fans, and otaku, it also touches on almost everyone of the genres within anime and I think does an excellent job of it, giving a great if slightly inane story for those that are willing to give this one the chance it deserves. I truly think UFO Ultramaiden Valkyrie will appeal to a lot of people, and a lot more then other reviews seem to believe.
Part of what makes this so special to me is the story which takes place on a Earth where aliens are commonplace, and neko girls (cat girls) are considered to be just as much a part of everyday life as the aliens. It is within this world that Kazuto Tokino decides to run his late grandfather's bathhouse despite protests from his parents and sister who consider it to be a "money pit". One night when working in the bathhouse an alien named Princess Valkyrie, who is running from a marriage her parents arranged for her, destroys the bathhouse when her spaceship crashes into it. She also mortally wounds Kazuto, however, she is able to save his life with a magical kiss that gives him half of her soul, and turns her into an 8 year old child. She can return to her adult form by kissing Kazuto, but it only lasts for a short time, and is mostly done when there is a need to protect Kazuto.
Princess Valkyrie is then stranded on Earth in the form of an 8 year old child with the mind of one too, unable to look after herself even though the entire solar system is out searching for her. Kazuto who owes her his life and truly cares for her works to protect this super sweet very hyper Princess Valkyrie from those alien invaders some who are searching for her to bring her back home to the marriage her parents had arranged. Valkyrie meanwhile shows a great and increasing love for Kazuto who shares part of her soul. Further Valkyrie's neko-meido (cat girl maid) Sanada comes to consider Kazuto as Valkyrie's official fiancée and helps him to protect Valkyrie.
Personally, one of the things I really like in this anime this switch that can occur in Valkyrie and how her different "ages" try to show how much she has come to love Kazuto, one is very sorry for what she has done to him and uses her powers to protect him, and the other, the younger Valkyrie, seems to cling to him jealously perhaps in a way to show how deeply her older self also feels but refuses to admit or cannot admit.
The animation is also stunning in my opinion, and very excellently done for such a short series which does actually have two sequels. Overall I say this is a must see for any anime fan and those looking for a good silly original anime that covers a lot of the genres of all anime within this one series.