Maybe I've talked about my nascent love for Johnnie To a bit before... =)
The Mission was fantastic, I loved it. Despite being made without a script (!), it holds together, even with its somewhat awkward plot development toward the end. Additionally, since it's not so dependent on a narrative, it doesn't have quite the same pacing weirdness of Exiled or Vengeance.
But whereas Exiled and Vengeance are super slick and mostly serious, and Election and Triad Election super dark and serious, The Mission is fun. The tone of The Mission is the lightest of any of the To films I've seen, with some really good funny moments.
And the music! It's cheesy, but I loved it, and I can still hear it in my head (in a good way). It sort of reminds me of something that would be in Sam & Max. A great scene, and a great example: the waiting game.
The five characters hired to protect the big boss are just really fun to watch; great characters and great actors, especially my To favorites Anthony Wong, Suet Lam, and Simon Yam. These Triad guys want to see some action, but most of their time is spent waiting. Still, there are some crazy stylish action scenes, and when they happen, they are welcome.
Definitely put this one on your watchlist; it is one that I will be looking to own.