Half-Life may be considered by many to be a true innovation of in gaming, but the game was - understandably - not always as pristine and cutting edge as it was when it released in 1998. Alpha footage of the game in its early stages reveals a different side to the game, and better yet, you can play the alpha build for yourself.
Here it is:
Note the part of the demo with the flying swarm. It sort of looks like this rumoured Half-Life 3 swarm technology video that leaked a year ago, doesn't it?
If you want to play it, Destructoid has posted a Reddit guide that tells you everything you need to do.