It was a really really good adaptation, a really good movie, and you should watch it right now. This isn't a review, this is just me saying things.
Like, I've seen it a few times already and it's still plenty awesome. They mashed like maybe the first eleven episodes together, along with parts of the OVA, and made a coherent story with it. Actually that's kind of a lie, they based it more on the manga because the anime has loads of silly moments, and the movie plays things mostly serious. Maybe underwhelming if you're used to huge Avengers, Star Wars, Transformers CGI explosive action, but it's really really well done action nonetheless. In fact, I'm pretty sure it's mostly wire-work and well-rehearsed choreography, not CGI.
The characters don't just play their parts well -- they ARE their parts. These guys look and act like real people. If I hadn't known this was based off of an anime/manga series, I would never have guessed it (but then, I wonder -- would I have watched it? I'm still thinking about how well this would go with ordinary film watchers as a standalone film). This means they toned down Kenshin's hair and scar and Sano's sword, among other things. The only thing I can REALLY complain about is a few of the fantastic elements -- the characters' special techniques mainly -- seem particularly out of place, and some of the camera angles to show these moves don't help on that front. Also, maybe it's just me, but Sanosuke comes back to join Kenshin on raiding Kanryu's mansion for no explained reason, and then it's never explained why he doesn't even join in the fight at the end.
It does what it's intended to, though, and it does it well. Lots of blood and violence, lots of familiar characters, lots of things mixed together and paced in just the right way. Orchestration (except for the pop song during the credits, which is still pretty awesome) works wonders for the mood, there's beauty in almost every shot, plenty of quiet moments and atmosphere. It's... quite refreshing to see a live action movie based off of an anime that WASN'T terrible. As I said, this isn't a review, this is essentially me gushing.
But please, PLEASE do yourself a favor. Please watch it for yourself.