Another fine film from Kim Ki-duk, although not in the same league as his two masterpieces The Isle and Bad Guy.
At its heart a simple revenge tale, it's elevated by an interesting psychological aspect that prevents it from being just another low-budget shocker. The protagonist is a put-upon street artist who meets an alternate version of himself who jolts him into action and convinces him to exact revenge on those who have wronged him.
Or he's the alternate version of a reclusive pseudo-guru who uses him to exact revenge on his enemies. It's not clear, but I'd bet on the former. The acting is very good all round, especially from the lead, and there are numerous comic scenes that don't intrude, but serve to lighten the potentially very dark drama. Worth a look.