Lol... why people rate this so low? Four and two, really? Considering this is one of Nagai's first work, this is very impressive. Not many new mangaka this day can achieve what Nagai did. He already had his style in this, and improved it in his later works. I think he blended the history and sci-fi part well. At first it looks like a common ninja story, but later it revealed there's 'other beings' involved in some conspiracy. And the sci-fi part doesn't feel forced at all. While it's not a masterpiece, it clearly deserves higher rating than 2 or 4 points.

The old school drawings doesn't bother me, Nagai draws well, and anatomically correct. It's his style after all. Old-school doesn't mean bad drawings; it's just different style, people. There's not much character development, except for Shishimaru. I think the pacing is okay, not too slow but not too fast either. The ending maybe a bit open, but I'm satisfied with it.

So, if you want a history mixed with sci-fi, try this. Nagai had interesting idea, and he executed it very well. Especially if you don't mind old-school drawings, you'll find more in the story.