Mucho ass-kicking abounds in this Donnie Yen thriller, but not until an hour in. Before then, we get a surprisingly taut, black-as-night police procedural thriller that depicts a hidden war between a gang of corrupt cops and a drug kingpin. These factors make KILL ZONE far more than the typical action thriller: it's actually an insight into the mind of a cop who will literally stop at nothing to see his man arrested. I enjoyed the way the film refuses to preach or paint characters in black or white; it's a film where dark alleyways are just as murky as morals and violent death is just around the corner.

It's also got an extremely dark, downbeat tone – I'd even call this film nihilistic. Despite all this, Donnie Yen insisted on inserting a couple of fight scenes in at the film's climax to appeal to fans, and they're the best you'll see out of all the films made in 2005. The first sees our hero tackling a brutal assassin in a famed 'alleyway fight' in which the blood literally flies and the choreography is top notch. Then Yen goes head to head with Sammo Hung, who's lost nothing of his skill over the years (even if he is bigger than he ever was before, physically). This final fight is by far my favourite, with elaborate fight choreography and bone-breaking stunts that never hold back.

Yen's character – more of a supporting role for much of the movie – features the actor at his most likable, with none of the pretentiousness I've witnessed in other movies. Simon Yam, a brilliant actor in my opinion, occupies plenty of screen time as the tormented, dying cop and gives a typically great performance. Hung, too, is multi-layered as the bad guy. The supporting cast is unusually developed – especially the aforementioned corrupt cops – and Jacky Wu has a stand-out, scene-stealing turn as the assassin.

I've now seen three films pairing Donnie Yen with director Wilson Yip. DRAGON TIGER GATE was the most disappointing, relying on special effects and wire work too much. KILL ZONE is the most adult, and probably the best made, with an original storyline for once. My money's still on FLASH POINT as the most purely entertaining, though.