It's not a great game, it's not a bad game. It's a time waster that builds itself on shock value and juvenile humor/antics. With that said, it you laugh at potty humor and the portrayal of things as "over the top", Postal 2 goes there and can be enjoyable. Let's make it clear, this is not Quake, Call of Duty, Counter-Strike or anything like that. The point is to kill things, lots of things and often in a rather creative way but this is not a gauntlet of ever stronger-growing hordes of alien monsters.
The game picks on a number of racial and social stereotypes. Chances are if you are easily offended by anything you wouldn't be playing a game where you could pee on someone and use your "unit" as a weapon in that manner. But if you are taken aback by religious and ethnic humor, this probably isn't a game you want to play. The violence is way over the top and the ways to kill people (which does get old after awhile) is fairly varied. The rag doll physics can make people die in some rather bizarre positions.
The add-ons, especially the Weekend mod, give a little extra variety and some small degree of structure to the "saturday" and "sunday" levels but shy of some new weapons, locations and "goals" for the days, it's pretty much more of the same. Again, it's not that Postal 2 isn't a bad game, it's just not a great game. It can kill some hours and is good for a few chuckles but if you are looking for something revolutionary, this isn't it unless your definition of revolutionary is something that can offend even the most liberal individual.