Minecraft I agree. Can't find the appeal either. It's a sandbox construction game. In 15min you've seen everything the game has to offer and you have to "invent" your own stories. Can be good for artistic types, but honestly they better invest time in real art application(2d/3d) than playing Minecraft.
As for Portal though, well, I don't understand your point. Puzzle are actually very smart (not stupid), story is great, humor is great, graphics are great, the game is smooth and bugless, level design and exploration is top notch. There's nothing dull about completing the campaign once. Few hours well invested.