I really like watching speedruns. It's really cool to see the sort of tricks and glitches people have come up with to get through the game faster. Recently this speed run of Half-Life was released, and its pretty cool. I'll note that this is a multi-segment run, by a group of people (you can see the current runner's name down at the bottom). So, its not a straight run-through, but its still pretty cool. Check it out.