Always late to the party, I finally just finished Portal. Actually I just got it, and then finished it in one night.
What a brilliant little game. Simple mechanics, the physics makes sense, the puzzles are not too daunting, they just require a little bit of thought, and the atmosphere is wonderfully creepy.
There are lots of little details that add up as the game goes on to make it interesting, like how your character has these things on her legs that help her jump higher, and survive falls from great heights (that's my interpretation, it's never explained.)
The story has great pacing. You get hints early on that things are a bit off, but when you find the first secret room it's starkly shocking and strips the veneer right off. The atmosphere changes abruptly, and it's a great example of storytelling in a game without using exposition, and letting the player uncover the story.
And of course, the computer guiding, taunting, threatening and wheedling you along is highly entertaining. The black humour is wonderful. The song at the end had me laughing so hard I was in tears.
It was short, but well worth it. Now I have to play all the bonus maps.
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