As Bill said, the Match hammer has a shallower sear notch cut into it. It also has more of a neutral angle to the cut of the sear notch (AKA hammer hooks).
If you watch really closely when you cock your standard USP 45 and slowly pull the trigger. . . you will see that as you pull the trigger, the hammer cocks a little more before it is released by the sear. This makes the engagement of the two parts a little more positive, and less able to go full auto by accident or wear. The geometry of the Match hammer has less postive engagement with the sear, such that when you cock your USP Tactical 45 and slowly pull the trigger. . . you will see that as you pull the trigger, the hammer almost doesn't move at all before it is released by the sear. The more neutral engagement and the shallower notch combine to make a nicer trigger pull & break with less creep. But it's engagement surfaces require very careful geometry to avoid unintentionally going full auto.