Two small but high quality maps, walkthrough/combat initially in the basement of Black Mesa (presumably). There's stuff to find, some lol moments, a nice balance of combat and exploration, and some very nice layout design - an unusually good balance of detail and closeness, without feeling cramped.
Whoever made it, it's a shame they didn't make more!
Playtime of about 10-15 mins, but definitely worth it. Minimal replay value.