Gravion, and its second season Gravion Zwei, is an anime that doesn't take itself too seriously - which means that neither should the viewer. Gravion parodies many other animes; the robot Gravion is obviously descended from Voltron; the aliens sent to destroy the earth are strikingly similar to the Angels in Evangelion; and the costuming and "harem" feel bear a close resemblance to Martian Successor Nadesco.
The plot is tried and tested. Aliens are threatening to destroy the earth! The only one who stands between humanity and extinction is Sandman, a billionaire with a vision. From his vision comes the birth of Gravion, a multi-component mega robot piloted by a group of young teens. Through constantly evolving enemies and the burden of teenage hormones, we get to see the Grand Knights conquer themselves and their enemies with style and a theme song that plays too long and too often.
The first season spends much of its time on limited character development and establishing the relationships among the Grand Knights. Many of the episodes felt like filler and though the viewer will have plenty of laughs, there will be many unanswered questions at the end.
It is not until the second season that Gravion finally reaches its stride. Details regarding the origin of the enemy and the mysterious Sandman himself are finally revealed, and the story moves forward full tilt. At the end of the second season, all loose ends are tied, and we are given a happy ending (a rarity for anime). The finale leaves the viewer with a sense of satisfaction that evil has been vanquished and that there is still hope for humanity.
Admittedly, Gravion takes a long time to get to the point, but it is fun, lighthearted, and enjoyable with a complete and satisfying ending. And let's be honest, who doesn't like giant robots?