I've seen a couple of To films before this one so I kind of knew what I was getting into. This may be a HK action film but it's nothing like the more loud and workmanlike fare that has come from there in the past 15 years.
Five men are called to protect a Triad boss who is repeatedly attacked by gunmen. The plotting is as simple as that. What matters here, as in any other To film I've seen, is the style and the contemplative pacing. Sure there are shootouts galore to quench the thirst for lead of the action fanatics but they're not all out bloodbaths or elaborate stuntwork. They're carefully choreographed and subtle in execution. The pacing might appear slow to people used to the spastic editing of Hollywood action fare like Bourne Ultimatum but therein lies the power of The Mission. You get to spend time with the characters, observe the camaraderie that develops between them, share the mundane parts of their job - it's not all glamour and glitz in the work of the bodyguard. In that aspect, I believe Johnnie To to be equal parts Howard Hawks circa Rio Bravo and Jean-Pierre Melville, albeit with a slick layer of HK style on top; nice suits, fancy cars, cool glasses et al.
The cast deserves a mention though. Anthony Wong, Francis Ng, Rony Leung, Simon Yam, they're all great in their respective roles, understating things enough to fit with the contemplative pace of the movie. The score deserves one as well; it's cheese-tastic in all its casiotone synth glory. I laughed the first couple of times the music cue played but then warmed up to it until I realized it's an integral part of The Mission's peculiar charm. If anything it lends character.
All in all this is a subtle action film, but thoroughly enjoyable. For a much superior execution of the same idea check out Johnny To's Exiled from 2006.