These games have two things in common. They’re short and portray a fairly cynical view of the world. In Portal, you play as something, probably some kind of artificial creation (well, it is a game-character), that has to play a series of games to get out. You are guided by a voice that encourages you, while subtly saying that you really mean nothing. You are test-subject that exists only to test the game, or perhaps to test your resilience to a game that is trying to kill you.
In the World of Goo, you are an observer that manipulates pieces of goo. Little tiny bubbles, which you can stick together, until a way out is found through a vacuum. Each level has a message from the Sign Painter, who again tells you what the purpose is, while also subtly pointing out that this is just goo, that, perhaps, we are all just goo, working together to find a way out.
The target audience for both games would be between 12 and 99, I would say. I would raise that up a little higher. Sure, life is a cynical beast and we are its beastmaster, but to pump our kids full with this message… I’m not sure what the pedagogical value of that is. Of course, if you win, well, then it makes more sense.
Time to finish one of these games: probably a weekend.
Quality of game-play: challenging, solid games that stay with you.