Forget outragious open world and prepare for broken linearity.
I principle, you can do everything you liked in postal 3 and much more comparing to postal 2. But here, and in third person, it just feels dumb and pointless.
The missions are much of the same and provide some funny weapons. The weapons are the highlight of the game. But if you have seen the trailers you know what to expect. Watching the trailers is more fun then actually playing the game since the action is very unforfilling.
There is simply no point in playing this game.
If you want a complete over the top game, play postal 2. At least that one is fun.