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.
The idea behind this mod is nice, as it brings the awesome gameplay of Sven-Coop to the source engine. The only prblems are, that the netcode seems to be bad, as there are often lags, the player are worse than rude. Also the number of servers is mostly >6, and the number of players is rough the double size of this. The levels also often lack a clear level design, sometimes out of the boringness of not knowing what to do player leave/being kicked for amusement.
+ many maps
+ different gameplay
-number of servers/players