I have never played half-life. Any of them. I have seen bits over the shoulder of someone else and thought they were kind of cool, but I do not play FPSes. I am not that sort of person. (My brain has trouble with first-person 3d.)
Therefore, while also thinking Portal sounds nifty, I am highly unlikely to ever play it.
But since some people wouldn't SHUT UP about quoting it, I have seen the ending song.
I am that sort of person. The kind that doesn't like not getting the joke.