!! This is a simple port to Opposing Force with addition of weapons and powerups from that game as well as some barnacle grapple spots !!
The HL1DM version
Black Mesa had constructed 4 portals to various locations. Xen was their main destination but for some reason the other portal are ending up in strange places.
This map has 4 areas connected by a main chamber.
Jungle, Snow, Xen and Offices.
Jungle is all about tight areas with emphasis on verticality.
Offices is all about corridor fights where everyone is on equal level.
Xen is about low-gravity fights with minor platforming and various routes.
Snow emphasizes on simple, open but balanced and fun shooting without any complexity to navigation.