It's not impossible to make a good live-action film based off a manga. Oldboy is a classic, Speed Racer has retrospectively been called an underappreciated masterpiece, people seem to like Ichi the Killer (though after seeing Audition i'm too scared to watch it), and there's also... yeah, there's not much else that's good.
Live-action movies based off manga tend to suck. Even when they don't fully suck, there's often something cheap or mediocre about them. Typically, American adaptations have lacked the care and Japanese adaptations have lacked the resources to make live-action adaptations that measure up to their hand-drawn source material.
Rurouni Kenshin, however, is one series that makes a lot of sense for Japan to adapt into a live-action movie, given that samurai films are a genre Japanese movie studios know how to do properly, even if they don't make them as frequently these days (what was the last really great one? 13 Assassins?).
A trilogy of live-action films based on the manga and anime series were released in Japan from 2012 through 2014. Now FUNimation is releasing the trilogy in the United States through a series of limited showings. The first film, Origins, played this week; Kyoto Inferno plays September 12-14 and The Legend Ends finishes it off October 3-5. One minor note: FUNimation's subs use slightly different translations from previous Kenshin releases. Reading "Battousai the Killsword" took a bit of getting used to, and doesn't roll off the tongue like "Battousai the Manslayer" in Media Blasters' translation, but certainly beats the embarrassing name "Battousai the Slasher" from Sony's Samurai X dub.
Speaking of "slashers", Kenshin totally has better chemistry with Sanosuke than with Kaoru, especially in this movie where Kaoru's part has been minimized. As a result of paring down four volumes of manga into one film, a lot of character development is cut out (Yahiko in particular is just... there, with no backstory or anything), but Munetaka Aoki as Sanosuke is the clear stand-out of the film's cast. Almost every line and action of his resulted in applause from the audience at the Landmark Kendall Square screening on August 8th, and it's easy to understand why.
The film's biggest challenge is with tone, trying to integrate the series' sillier humor into a serious storyline. Sometimes it doesn't completely work, a reminder that not everything translates so well to live-action (and that the humor in the manga and anime hasn't all aged brilliantly to begin with). However, Aoki is the actor who best achieves the proper mixture of wacky and serious. He's broad and a bit campy, but with such intensity and dedication that it never detracts from the drama of the story and in fact makes it all the more compelling.
Does Rurouni Kenshin: The Origin end up falling under the "cheap or mediocre" curse of live-action manga adaptations that's claimed series from the likes of Death Note to the more recently released (and heavily hyped) Attack on Titan? Fortunately no...but it's not without its criticisms. While the production values are mostly solid, there are some traces of cheapness.
The most notable issue is that, while Takeru Satoh fits the part of Kenshin as a 28-year-old, it's really distracting seeing him play Kenshin as a 14-year-old in a flashback sequence (then again, it's not really more distracting than the Japanese voice actress in the anime not even trying to sound like a man).
However, despite the film's flaws, its story, characters, and action elevate it above mediocrity. The screenplay does an admirable job condensing a lot of story into a single cohesive narrative, shuffling around some parts but staying true to the manga's vision of a story dealing with heroics, idealism, and redemption. Even if there's less character development as a result of the condensation, the portrayal of the characters still feels right, and their looks and personalities feel straight out of the manga.
The best thing about the movie, and what should give it entertainment value even to those who aren't fans of the source material, are the fight scenes. They're what you go to a samurai movie for, and this movie doesn't disappoint. The second half of the movie is relentless with them, and boy do they impress. Which scene's the best? Is it when Kenshin fights a gunman with a sword? Or when he fights a gang of swordsmen with his bare fists? How about Sanosuke's kitchen battle (easily the funniest bit)? How about the crazy wirework when they storm the mansion, or outrun machine gun fire? Or the intense final duel, the biggest test of Kenshin's no-killing ideals? This is one area the movie can actually surpass the anime in some ways, free from the need to drag out battles over multiple episodes and able to pick up the pace.
As someone who was a serious fan of the Kenshin anime back in my tween years, and one of the first anime I got into, this live-action movie was satisfying. The Kyoto arc is when the series gets really good, so I'm looking forward to seeing how the next two movies adapt it.