Definitely nothing like the stale Hollywood action genre. Energetic, stylish, and just the perfect length. That said, the cheesiness of the b&w flashbacks and the music choices add a bit of a comical effect, which was probably unintentional. I can't say the characters were particularly interesting, either. The ending won me over, though, and I might just check some more Hong Kong action.
Rated The Departed the same, although I prefer this to Scorsese's remake. IA is a much leaner affair, w/ none of the unnecessary bloat of the Wahlberg and Nicholson characters. Lau's character in IA is much less two-dimensional than his Matt Damon counterpart in TD, but DiCaprio's character is better fleshed out than Tony Leung's. I did like TD's twist of having both men involved with the same woman, but IA is sleek.