“You are the Corporal Daniel Shephard, after crash landing on your way to Black Mesa, your brother Adrian became a Corporal in less than 3 years, very few people have ever become a officer that quickly. As a lowly grunt you have been given the perfect oppurtunity to prove yourself and show that Adrian isn't the only successful one in the family. Escape an infested research facility with aliens and a whole battalion of Black Ops... its going to be hell." This was originally created by B-dama (see his readme for contact details)
This review may contain spoilers
Awesome mod, never felt bored while playing it. Really the best I've played for Opposing Force alone. I highly recommend this one. Great level design, pretty tough to beat but isn't impossible. Also, I really like how you can have your allies follow you pretty much from the start to the end but it isn't necessary. Even when there are parts when you have to leave them, there's always an option you can find to open the way for them. Which is awesome for making those firefights more intense and fun. If you haven't played this one yet you should definitely consider it. All the classic Opposing Force weapons and enemies in a new setting. Isn't the longest mod but I would not consider it too short.
Try it out if you haven't yet.