There are a few good kills and lots of messy blood at the end but I suggest fast-forwarding to get to them. There is nothing worthwhile at all to learn or enjoy before them. It's impossible to gather up anger at the bad people, in order to get on the revenge bandwagon, because the bad people are so bluntly impossible to take seriously the viewer reels in disgust at how badly they are drawn and how immaturely the film is conceived, instead of wanting them killed. It's not a question of moral outrage. This film doesn't push buttons by pushing any ethical envelopes. It's just low-rent, poorly done, unimaginative, middle-school-dropout-level acting and scripting. The director's vision is childish.
I'm dismayed that this is the kind of slop South Korea is going to pump out for the world stage. This film isn't even good enough for a straight-to-video release here in the USA. The problem is, it's got typically solid South Korean production values so some folks may be fooled.
If you want to see something recent in this genre from South Korea that's good, watch 2009's Missing. Heck, the first Death Bell is better than this sophomoric pile of fecal matter. Of course, so is I Saw the Devil (at least marginally) because it, along with Missing and to some extent Death Bell, employed professional actors, i.e., actors who would have turned down any chance at being part of this film.
[UPDATE] To be clear, I'm not against what this film tried to do. I'm against the fact that it did it so poorly. To test my resolve, I watched the remake of I Spit on Your Grave after watching Bedevilled. It's not a good film either but it's a lot better than this. They are pretty much the same film: rape and abuse a woman and then watch her get revenge. The notion that this film has any social commentary value is bullshit. It's nothing but cheap exploitation cinema written and executed poorly.
Dread Central and Brutal as Hell (think it's a masterpiece)