Anyway, last night I reread the whole 7 volumes in one go. Just to see whether my perspective of this change over the years.
Surprisingly it do change. Lots of things I didnt notice before. And indeed this manga is fun, coherent, and noticable.
On one level this is a manga about the resistance of human against the clearly-superior-in-tech aliens. Even the best weapons mankind has to offer doesnt stand on par with its alien counterpart. We die in big lots, the strongest nation (USA) get a heavy beating in both military and economy, and the end game is pretty much a draw, as in we cant kick the aliens out of Earth.
On another level, it's about the growing up of a hero. A boy who live pretty much normally his whole childhood now has to do the growing up in days, from an innocent to a killer. If at any time you feel irritated with Hoichi, count back that day to the start of manga, I guarantee you not much time has passed.
On one big level, it's about the grant figure of Hosuke. He's one ruthless bastard who never forget the disparity between his (and Earth's) forces and alien forces and literally do anything to lead Earth to victory. He train his sons to be warriors and leaders by pushing and pushing, snap both of them but at least his younger is made of sterner stuff so the boy snap back, the older was brittle and so died an ignomiously death. And he's a great leader too, his harem notwithstanding (All the girls have great abilities in all cuttingedge techs). Tactics, Strategy, Politics, Foresight, all that is requirements of leader he have.
All in all it's a recommended manga you should have.