Portal didn't have much of a story to it, so I would agree that The Witcher's was better, but Ep2 did and it was, imo, a better experience than The Witcher (which is also very good).
In my book, Great Material > Good Material, regardless of originality.
I hold originality to be of much greater importance but with games it's more about how it is delivered, rather than the actual story. Half-Life 2 didn't have a deep story but the way in which is was delivered made it stand out - Ep2 took that delivery, improved upon it considerably and added a decent plot to it. The Witcher also did a good job but the voice acting, character animations, etc, were not as expressive or polished.
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Founder of the "I Hate Smiley Fitz"
Riley has autism. He has trouble communicating, and in an overstimulating
environment, he can get frightened and run away, leaving his parents frantic. - Auburn
"The price of freedom is eternal vigilance."