Actually, Lucas' first 1973 treatment was a literal remake of the film, and Lucas even copied entire passages from its summary in Donald Richie's famous book The Films of Akira Kursawa (probably because he didnt have home video and couldn't remember every plot detail). But yes, the final film deviated quite a bit, more than enough to constitute a unique entity in its own right. Still, the similarities were such that Gary Kurtz contemplated purchasing the rights from Toho just in case. I like to think of it as "inspired by" rather than a remake.