Personally, I didn't like it all that much. The concept seemed a bit corny to me, though I've gotta say that the action sequences were nothing short of jaw-dropping. I didn't really buy the whole concept of "gun-kata" (statistical probability allows you to dodge bullets? GO MATH!), but I guess it's as good an explanation as any.
I wasn't too impressed with the acting, particularly from the main character. He seemed incredibly tense and wooden throughout the whole film, and in some of his worse moments I kept expecting him to come out with a line like "Whoa, I know kung fu!"
All in all, I guess it was a decent action film, certainly no worse than about 90% of the repugnant crud that comes out of Hollywood these days. Be warned though: this felt like the longest movie I've ever seen. I could have sworn that by the end of the 2 hours (ballpark guess on the length), I could have sworn I'd been in there at least 3 or 4.
Ah well, some people seem to like it, and more power to them I guess.
edit: typo