The politeness of the NPCs isn't so strange when you're poking around in a corridor or exploring a building and one of them gets in your way. During combat, however, it can be a little surreal.|
The first time I saw it in action was during the lighthouse standoff in the Sand Traps chapter. There was complete chaos. The Combine dropships were unloading soldiers, who were throwing grenades and peppering the outpost with pulse fire. The rebels were taking cover, and running here and there (since it wasn't squad combat at that point, they weren't follwing me around).
One of the dropships took off as I was darting between buildings, and it opened fire on me. I bolted for the door of one of the buildings as the dropship spit pulsefire all around me, shattering windows and splintering wood. I opened the door and lunged inside, my health just about gone, and ran smack dab into a rebel on his way out the door.
He said, quite brightly, "Pardon me!"
It was a very odd moment.
The NPCs in HL2 do tend to be pretty codependent and don't give you much room. You can send them away by pointing your crosshairs at a location and pressing the 'C' key, but it's usually only a few seconds before they come running back and clustering around you again. This isn't a big problem outdoors, but when you're in a narrow hallway or a small room, the crowd does tend to get underfoot.