Zombie Panic: Source is a such fun and addicting Mod thanks to its solid game play. The game play in this game is awesome. The game starts off hard , once you get to know your way in on the maps you will improve a lot. The maps are really interesting and get better each round you play them. The best way to survive is staying as a group to protect each other while doing objectives.
Highly recommended, especially if you play with a group of friends.