I'm a huge Tsutomu Nihei fan, but his Knights of Sidonia never quite pulled me in. I skipped the series even when I had easy access, and never really bothered with the manga. Maybe it's because it's one of his lighter/more commercial works, but when I heard Seshita was doing a film, I was willing to give it a go.
The setup reminded me of Gunbuster, though a bit more intricate and not as focused on the school part. The film revolves around a group of trained clones, who pilot heavy mechas against a race of space aliens. Humankind is aiming to colonize a planet, but the aliens aren't having it.
The animation quality is not up there with Seshita's more recent films, and the film's TV roots are a bit too apparent. There are still some very cool designs (the aliens in particular), and the plot won't disappoint sci-fi fans, it's just that I was hoping for more, after the Godzilla and Blame! films.