Nice find! I personally learnt the source engine from 3kliksphillip on youtube back in the days when I played Counter-Strike: Source, and I have to say he's great for teaching the fundamentals of level design, especially because he has such a solid knowledge of the engine and a great workflow.
I find it pretty hard to find good tutorials on unity, but this may be it!
Also, here's 3klikphillip's youtube channel:
http://www.youtube.com/user/3kliksphilip