Cadaver might know more, as he has played it longer than me.
Yes, considering I used to be an admin for an Insurgency server before I ever joined CTC.
It is simply this: One side is the Marines. The other is the Insurgency. You play in Iraq based maps. You are limited to certain weapons by character class. There are 4 classes per side. It can be run as team death match or by taking objectives in a map. Typically there are 3 to five objectives to capture per map. Objectives maps work one of two ways: Linear (Take objective A, then B, then C.) or just take all the objectives, not in a specific order.
It is similar to CS:S, except there is no bomb to defuse. And there is respawning during the match. And you die a lot easier. One shot one kill is very possible, even without headshotting the opponent. Ammo is limited, though there are ammo crates in game.
Typically you are limited to your battle rifle, pistol, and a couple of grenades. No 20 different weapons. You can pick up weapons from your dead enemy or friendlies.
RPG is quite fun, and an easy to shoot, and is a noobs firearm. The L1A1 is my favorite (Great Britian's edition of the FAL.)
Oh, it was the Half Life 2 Mod of the Year in 2007.
http://www.moddb.com/mods/insurgencyhttp://steamcommunity.com/games/InsurgencyThe original creators of the mod look to be making a new (unfortunately pay to play) version, soon.