Portal is really nothing that progressive thinking can't beat after a certain period of time. It's not so much hard as it is something that makes you use your brain.
That said, there's gonna be a chamber or two that you'll get frustrated by.
Quid Plura said:
The appeal of the game isn't the difficulty, it's the story (which is the best reason to play the game).
Sorry, what? The best thing about Portal's story was the fact that we knew so little about what was going on, and we didn't know about what GlaDOS' sinister plans were. It was pretty bare bones, but the mystery made it worthwhile.
But don't get me started on Portal 2's story, which appeared to be written by a team of attention deficit monkeys trying to get the biggest laugh on open mic night who have no concept of plot cohesion.