A small add-on.
Special Delivery is an add-on to Postal, offering 4 new levels. There are new characters and voices to go with them, and they are quite diverse, ranging from a supermarket to a city district ravaged by an earthquake to a lawyer's convention at a posh resort. However the levels are no more interesting than the 16 you had with the original game, so there is very little play value in this package. The levels are easier than the harder ones of the original, so you can beat all of them within less than an hour even on Insane difficulty. The original game had nothing to really motivate you beyond a few stages, and the add-on doesn't fix any of the bugs or improve the AI. It doesn't really matter these days since practically every place that sells the game will throw in Special Delivery for free, but at the time of its release it was a poor offer.