Here's what I liked about Portal 2 (can't speak for Portal as I never played it). It was highly original, and no other game has made me feel smarter, or dumber. It takes a while to get used to, but they set up the game so well, that it takes you through and points out the various things you can do with the portals. Every level is set up to test something new that can be used in later levels. You don't even realize how much you understand the game, until you watch someone else struggle their way through the first few levels.
Humor wise, this was one of the funniest games I have ever played. This game really has it's own charm and wit that really makes it a worthwhile play. Here's a quote that I (somewhat) remember from co-op. "In order to get ready for human testing again, I went through some old suggestion cards. You want to know what the number one suggestion was? Less deadly tests. That's absurd, how do they know if the tests are deadly if they're still alive to write the suggestion?" It might be funnier in the game, but it's full of those kind of witty sentences.
I don't mean to advertise, but I think it's a worthwhile play. I mean, it's a family-friendly puzzle game that became extremely popular in a realm full of bloody, violent fps games. That has to say something.