Ok, I have to say that I really like this game. It's very similar to the Wing Commander : Privateer model of a golden path where you have an open world, horizontal gameplay and character development with a game story waiting for you to follow it.
There's trading, truck upgrades, modular weapons, towns, factions, and an open world map to boot. The graphics are 2006-ish but if you're looking for gameplay, you can look past that.
The vehicles themselves are based around chassis that have stats but each chassis also has multiple front and back body components which different turret / upgrade / cargo slots. Not all weapon slots are 360 degrees which adds a positional element to combat.
The game won't work out of the box for Windows 7. You have to delete the videos in your Steam\SteamApps\common\Hard Truck Apocalypse\data\video directory.