Here we go in decending order, with Honorable Mention first.
Cowboy Bebop, The Series Shootout Finale
It ends around the 5 minute mark and contains more explode-y stuff with such style in that time than most action movies ever do. Note: the only reason this doesn’t count into the actual listing is because it’s from a TV show, not because it’s animation.
5. Exiled dir. Johnnie To- Opening Shootout

A classic throwback to old Westerns, done with such style. The entire movie’s excellent by the way and there’s actually a better shootout around the middle of the film, but I can’t find that on Youtube, so deal.
4.Leon dir. Luc Besson- Police Shootout

First, yes, that is a young Natalie Portman. Second, come on, it’s Jean Reno being a hitman ninja and what’s more awesome than that (besides the next three items on this list, at least in my opinion)?
3. Heat- Downtown Shootout

Trivia: All the sounds are from the shoot, they’re not studio made. Also, you can’t help watching it today and laughing at the irony at seeing who Robert DeNiro’s driver is(lol, they’re not in good hands). And, come on, it’s Al Pacino versus Robert DeNiro.
2. The Wild Bunch-Final Shootout

This clip is 40 years old. Really makes today’s action movies seem lazy, don’t it?
1. Hard Boiled- Hospital Shootout
Before I put up the clips (yes, plural. The scene was too big for one youtube vid), let me just say that this entire list could have been made by scenes from John Woo Hong Kong flicks, and half of them would have been from Hard Boiled, which is essentially an action scene, some exposition, a bigger action scene, more exposition, and ginormous action scene. This is the ginormous (including a 2 and a half long take of Chow Yun Fat and Tony Leung killing people at the beginning of the second clip)



Yeah, that scene totals about 26 minutes. Yeah. The entire 3rd act is a shootout. It also has the most badass baby ever put to film. Baby’s being held by Chow Yun when he gets shot, and the baby gets blood on its face, he’s all “whatev” Then laughs it off to Chow Yun saying “Yeah, you just killed a bunch of people in front of my infantile eyes. That was awesome.” A few minutes later the baby puts out the fire on Chow Yun’s legs by peeing on. Just to repeat, the baby PEED OUT A FIRE. His dad must be half Chuck Norris half Bruce Lee, and half Jackie Chan, with a dash of Chow Yun Fat for good measure (Yes, the baby is that badass he defies the rules of math)