Obsidian Conflict is a cooperative multiplayer modification set in the Half-Life 2 universe. It features a large amount of new gameplay features on all-new maps specially designed for the mod with focus on cooperative gameplay, as well as over hundred user-made maps following the same formula. In addition to that, You're able to play through vanilla Half-Life 2 all the way up to Episode 2, as well as experimental support for cooperative Half-Life: Source play.
This mod is one of the best co-op mods existent for HL2, it has great moments, varied levels, and the ability to play HL source (an ability that Synergy lacks.
There are some complaints.
1- This game needs more playermodels and to tone down the HL2:DM playermodels (not every one wants to be a rebel or a combine), and also an updated playermodel browser (for people who find it hard to switch playermodels).
2-Alternate animations and viewmodels (for the HL2 weps at least).
3-Default access to the ep2 models/textures (for those who dont own ep2).
These are th only complaints however.