One of the toughest maps in the campaign. Traffic is high at and underneath the railgun platform, and there are some short loops you can take around there to grab a yellow armor and some health reloads. The map's average encounter distance lends itself well to the lightning gun, and to a lesser extent the rocket launcher and shotgun. The railgun is good here too if you're quick with it in medium-short range.
The original Kaos was used as a bedtest for shaders. That glowing lava, for example.
There's a secret place in the map. You should descend to the lava pit, search for two pillars and shoot the wall between them. This area contains an easter egg and the Invisibility item. It was present in the original Kaos by Vondur, and was carried onto OA.