I won't go on at length about the film, because others have already done so, and well enough.
I will add my opinion about the ending, though.
Let me begin by saying that I understand the film was intended to be the first part of a trilogy, and so the unresolved ending could easily be attributed to a "cliffhanger" ending that might be resolved in a second film; however, we don't get the rest of that trilogy, so we must contend with the film as a complete work of art.
With that in mind, I propose that the unresolved ending of the film - the sudden, freeze-frame ending, still within the throes of an unfinished combat - is meant to suggest this:
:::Ryunosuke has actually died at some unknown point during the final sword battle; what we are in the process of observing, then, is Ryunosuke in his own real and private Hell, an afterlife of endless opponents, brutal killings, and constant injuries to his own body, none enough to kill him, but enough to cause him pain and torment:::
The reasons I see to accept this idea are several:
1) The inn is now on fire; fire is an easy metaphor for Hell (certainly for Western audiences, but possibly for Eastern ones as well). As to that fire, no one is responding to it directly, as people would tend to do if a well-populated inn was burning. There is no sound or image of commotion, shouts, running for exits, etc., as we usually see during burning-building scenes, even when there is a battle going on.
2) The scene immediately before the final battle is focused on ghosts and hauntings - it begins with Omatsu telling the tale of the courtesan who killed herself in the now-unused room, and quickly proceeds to multiple images of Ryunosuke fighting the ghosts of his own victims.
3) The room that Ryunosuke is in, and proceeds to tear apart before the attack of the samurai, becomes almost supernatural - the curtain walls he cuts through are endless, repeating, circling back upon themselves - he cannot escape this room, even by cutting his way through and out. Then, the rooms of the inn he fights his way through become endless, maze-like, and repetitive, with no occupants except the endlessly attacking samurai.
4) The final freeze-frame suggests to the audience that there is no logical ending to this scene; indeed, it never ends.
So there you have my interpretation of the ending of "Sword of Doom". If you like it and ever quote it, please give me, and this review, the credit!