Opposing Forces is a straight-forward and simple capture the flag map. The texturing and geometry of the map are pretty basic, but at least there are no missing textures or other big technical problems. The most noticeable issue is the rain. It falls in the flag rooms but not in the center of the map. I believe I did this in order to avoid framerate drops.
Each flag room has a plasma gun and yellow armor. There is also a water filled pipe you can swim through that will open up to a small room containing a railgun and a teleporter. This teleporter will take you to a high up ledge above the flag for an optimal camping position. Two corridors coming off either side of the flag room connect to a larger room with a shotgun and a q3ctf2-inspired mega health alcove. The shotgun room is connected to the center area, where there is a rocket launcher on ground level and some stairs on either side that will take you up to a platform where quad damage spawns.
The rain, thunder, and lightning make for some pleasant atmosphere, but the simple layout and rather boring gameplay probably won't be enough to keep you interested.