Personally, this is my favorite Ichi movie. Any fan of the series will enjoy this, because it has what you've come to expect from Ichi. As for people new to the series, if you don't like this one you probably shouldn't bother with the others.
As always, the sword choreography was above par. Katsu's blade passes through untold scores of ne'er-do-wells, and the number of adversaries in the climactic fight is cause for alarm, even if they are facing down Ichi. For those of you placing a high importance on sword choreography, I would like to mention that this movie contains a a style I've only ever seen once before, in the underrated 'Sword of Doom'. The 'soundless' form used by Ichi's counterpart is more than impressive, and action followers will want to see this movie just for that alone.
The acting in this particular film is also worth note. Katsu is always incredible as Ichi, it goes without saying, but the real goods here today is the intense performance of Tatsuya Nakadai, playing a nameless ronin. Were it not for Shintaro's genius, I would almost say Nakadai stole the show from Ichi himself. The unrelenting conviction of the nameless ronin is done brilliantly. If you've seen Sword of Doom, it is essentially the same character as Ryunosuke.
The acting from the rest of the cast is decent. There is one female of note, but I was left unimpressed by the primary enemy, and no characters other than Ichi and the ronin left an impression on me. Fortunately, either one of those two more than make up for it, and in fact interactions between the two are some of my favorite scenes in film.
There is a scene midway into the film which seems to have been the basis for the musical choreography we saw in the Beat Takeshi 2003 movie. Kinda fun.
So my final verdict is a hearty smile and a cheery thumbs up to anybody who does not follow the series, an enthusiastic outburst for those who do, and a 'definite must' for anybody who really liked Sword of Doom, since this might as well be kind of an unofficial sequel. The acting by the few was unbelievable, the choreography as good as always (perhaps a bit faster than earlier installments), and the two story arcs came together in an exceptionally satisfying way.
I consider this a first tier movie.