reason this film is great

No, it wasn't great. Barely good. And there's NO bloody reason for it to be nearly 140 minutes long. The battle scenes go ON and ON and ON long after they could have made they're point, and the choreography and design of these sequences--even for Japan, circa 1979, are clumsy and repetitive. These sequences NEED a sense of the strategies being employed by either side in the battles (especially the seemingly endless climactic war), but instead they're just scene after scene of massive numbers of extras running onto a big field while smoke bombs and strangely dusty explosions go off around them, sending them flailing, while Sonny and his boys act all macho and/or scared as they gradually run out of ammo, fuel and vehicles. Watch the guns of the soldiers during these sequences, 90% of the time there's no muzzle flare, just sound effects.

And for those who think Chiba and co. decide to use their superior weaponry for domination, think again: they ONLY use the weaponry to wipe out the enemies of the power-hungry general they befriend. When all the toys are largely gone, and Sonny beheads the enemy leader, only THEN does Chiba declare that the will end up ruling the era, in part because he knows he and his unit are never going to get back home, and in part because he knows such a declaration will draw the wrath of the general they aided, and indeed this general ultimately kills Chiba, with the remaining troops getting theirs soon after. The fact that their corpses are given respectful treatment, and NOT severed heads, is key. The general still respects them, and more than likely knew they could not have taken control of the land. But custom dictated that they must die.

Regardless, this film is an overblown B-movie. Good concept, but the execution was lacking severely. And the special optical effects during the Time Slip . . . ugh!