SMOD is a single player mod of Valve's first-person shooter 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.
A great weather change for half-life 2. new weapons, new enemies, gore effects, bullet-time are great. but some bugs, occasional crashes, uneven difficulty keeps it from being perfect. still, you should definitely give it a try. it's very fun and bloody.