Now, this has been free for a while on GOG (and on Steam) but seems to not have been posted when it went from paid to free on 20 December 2019 on Steam so here is the post.
Game is old but rated "very positive" on Steam. Not sure if you still can get trading cards but probably not if you only got it after it has gone free (I did get it before so I got cards and cannot check myself now).
From the website:
Take control of The Postal Dude in his infamous first outing as he battles to survive in a world gone mad! POSTAL is a classic isometric shooter filled to the brim with fast-paced explosive action. Crazed gunmen out for your blood await you around every corner, and your only choice is to get them before they get you. Fight back with a destructive arsenal as make your way through a violence-stricken town.
It's time to go POSTAL!
- New control options - use your mouse or dual analog sticks. None of that tank control insanity!
- Get your friends together for LAN Multiplayer - co-op or deathmatch for up to 16 players.
- Blast your way through 22 levels: Includes the original 16 level campaign, 4 from the Special Delivery expansion and 2 previously Japanese-exclusive levels.
- Test yourself with one of 22 bonus Challenge stages, across 4 categories. Or play through all of them in The Gauntlet.
- 9 devastating weapons: Defend yourself with varied tools of mayhem. Take aim with the Scatter Gun! Clear out rooms with Grenades, Mines, and the almighty Napalm Launcher! Whip out Heatseeker Rockets for those big groups!
- Wide range of foes: Defend yourself from Molotov-tossing Grenadiers, gun-toting Infantryman, rocket-firing Heavy-Weapons Experts (don't forget to duck!), and angry Ostriches!
- Non-stop, guns-blazing, adrenaline-fueled action!
- Fully-voiced Japanese audio available!
Enjoy!
Pity its not Postal 2.
The only good game that encourages running with and throwing scissors.