Chances are, you've never really seen anything like Gasaraki. Probably because there isn't anything really like Gasaraki.
Gasaraki is a show about politics, a family, spirituality, mechs, and more politics.
The show opens with a test of the Japanese Special Self Defense Forces' new Tactical Armor, a bipedal weapon with unprecedented mobility in an urban environment. The mechs are very well-designed, and look like the sort of thing that the US military might actually produce.
Then we are treated to a Noh dance, being performed by one of the pilots of the Tactical Armor. During the dance, bizarre phenomena occur, including gravity increases, and a girl appearing to him in a vision, begging him not to bring back "the terror."
And then we learn that the pilot/Noh dancer is Yushiro Gowa, one of the children of the Gowa family. The Gowa family also just happens to be developing the TA for the army.
And that's just the first episode.
Much of the show is produced in a style similar to the news coverage of Operation Desert Storm in 1991, further adding to the realism of the situation, which includes the US invading a (fictional) middle eastern nation which appears to have developed weapons of mass destruction.
The animation is uniformly high quality, fluid and clean. I've never seen a show produced for television that looked this good.
The show was written by people who actually understood politics, and that is a breath of fresh air. With a complex geopolitical scene as a backdrop, Gasaraki constantly has surprises for the viewer, as well as the constant sense of mystery surrounding the "terror" of a thousand years past.
Some have compared the show to Evangelion, but such a comparison is flawed. Gasaraki is much darker and more complex plot-wise. Where Evangelion is about Hideako Anno's personal views on spirituality, Gasaraki is about politics, with a dose of spirituality to add mystery. Beyond the obvious similarity of mecha and spiritual elements, there's really no comparison.
In summary: Gasaraki is not for those with short attention spans. Gasaraki will reward those who pay attention to detail. Gasaraki is a triumph of substance over style, a rarity in the world of anime these days.