Okay, let me start by saying what Law Don isn't, it's not A Better Tomorrow and it's certainly not Young and Dangerous. Law Don has a lot of what you might expect from a 70's modern setting kung-fu picture (just not as much kung fu).
Alan Tang is great in the central lead and the film is mainly designed to highlight his strengths as an actor and in that sense the film delivers. The story is a less than perfect re-working of the Godfather pictures and Tang is nothing more than a thinly veiled Michael Corleone (Al Pacino in the Godfather) with a HK twist.
The action is plentiful, but nowhere near as stylish as the stuff you'd see in a John Woo classic (in fact the action greatly reminded me of another film from this era called Super Dragon's Dynamo). But, if your looking for something fun and undemanding, give it a try.

-Jay