http://www.youtube.com/watch?v=GEC45BH6w6I
It's worthy a watch, I've never thought that they put so much stuff just into one room.
the only thing i can think here is
no shit
source is based on quake engine and the .bsp level design which was invented purely for closed space fast-paced gameplay with some puzzles thrown into it to keep the players busy.
thats the entire "analysis" for the gameplay in hl and 40 mins isnt the most optimal time to describe it.