SMOD

SMOD (short for SuperMod) is a single-player modification that adds new effects, weapons, and NPCs to Half-Life 2.

The new content consists of many new NPCs and weapons, new gamemodes, comprehensive customization and tweaking options, new abilities for the player, and new features to the gameplay, such as level randomization and simple branching in the otherwise linear flow of the main episodes.

This is a Japanese modification for Half-Life 2 that certainly throws some suprises your way.