Rather than focus on the original Japanese version of this movie, which is pretty much the same as this arc during the series, only worse, I decided to focus on the dubbed version. Keep that in mind, please.
If you have ever watched the anime of Gintama, you would probably think of it as something that really wouldn't work in a different language. While American reference comedies work in countries other than America, since most references are universally known for one reason or another, Gintama focuses mostly on referencing different anime/manga franchises, TV personalities, or voice talents that would go right over the heads of Westerners that aren't "In the know". Because of this, hearing that Gintama's movie was going to recieve an official dubbed release was, odd, to say the least. (My cries of WHAT?! Seemed to warrant a visit from the neighbours...)
And while, yes, the arc of the story that this movie covers is very light when it comes to references, but it still seems stange to me. Even without all of the reference comedy, Gintama in English will still be too esoteric to appeal to people who aren't already well invested in the series.
If you've seen Gintama, you already know the story in this arc. Sakata Gintoki, former rebel samurai, gone freelance for hire and his two young friends Shimura Shinpachi and Kagura were hired by sibling swordsmiths to try to find the extremly dangerous "Cherry Blossom" made by their late father. At the same time, numerous wandering samurai, or, "Ronin" have been reported dead on the news. This arc introduces new antagonists to the series, with Takagi Shinsuke and the rest of the Kiheitai. I enjoyed this arc immensely when I first saw it, and while the movie rushes through most of the details, it still serves as a good way to refresh one foggy-headed viewer's memory.
(Also, this one had some scenes that the original one didn't, though they're more... related to the fact that's it a movie, not related to the plot.)
I really enjoy Sunrise's work on Gintama, and while this is simply a retelling film, you would expect more new than you really get animation-wise. The characters have always looked great, but the detail in backgrounds rarely goes beyond what you've already seen, and the very few redrawn scenes there are don't push push beyond, say, 2011 TV Gintama. Colours are nice and clear, and the action scenes are fluid, but nothing from this film really show that it had better production values than the TV series.
Here's one area I feel conflicted with. I should hate the voices in this film. Some characters sound as though the voice actor behind them had no interest, some characters sound as though the dub company just kidnapped random people off of the street to voice certain roles, and some were just given the wrong voice. Even so, I can't say that I disliked the voices in this. It wasn't like Bible Black's "So bad it's amazing" voice talent, but the voices felt, to me, so right, yet so wrong. I don't think characters were miscast (In most cases), really, I just think any English voice would come across as being "Wrong" in this case. Chris Patton's Gintoki is strange, but not in a bad way, and most of the other characters are voiced in an unusual, but charming, way. A fair few swear words were poorly stuck in the script for good measure, which I found off-putting and I do recall a slight cringe here and there, but that's more due to the script, not the reading of it. (Though I didn't like the use of honorifics. I always hate that in English dubbed things.)
I think the characters in Gintama are great, but none of them go through any real development throughout the course of this arc. A little bit of backstory is touched upon for Gintoki and some of the other samurai in the series, but most of the important details after the time this movie was set. The English script takes a few liberties when it comes to some of the dialogue, making some characters, more or less friendly or agressive. Still, most of the humour comes through unaffected.
Overall, the movie is a mere re-telling film with little new, but a whole lot of same. But when I watched it in English, it felt very different. It felt... new. And that made it much better than watching the Japanese one. I have doubts that this would interest too many people to give the series a try based solely on this film, but I don't think that's the point. This feels like a "for the fans" sort of thing, and while I know for a fact that many fans of Gintama would pass this up simply because it's a re-telling of an arc, I would say anyone that likes Gintama should give this a try, especially if you're already planning on watching this movie anyway, but are putting it off (Much like I was), simply because it's a re-teling, then watch the dub. It's pretty hip, I daresay.