This is the best video I've seen in a long time. It's inspired by Half-Life (though you probably know that by the title), has amazing cinematography and amazing special effects. Overall, I'm shocked and pleased. I really can't say anything else about it. If you like Half-Life or have even played it, watch this trailer. Even if you don't, just watch it. It's amazing.
I discovered it from Bob's House of Video Games, but it has it's own homepage so please click there to BeyondBlackMesa.com.