Lateral thinking...?
Oh, hello!
Portal is short. Like 3 hours or so short. But it's a self-contained story, with no expected knowledge or to be continued ending. In short, a perfect weekend game. Anyway, Portal is all about its main mechanic: The portal gun. The portal gun does two things: It shoots a blue portal (with the left click) and an orange one (with the right click). Now, that may seem complicated, but bear with me. Now the hard part: If you go into the blue portal, you come out of the orange one, and vice versa. Yeah… It's quite complicated.
What Valve does well is the context and the story. Basically (No spoilers), you are going through test chambers, going from A to B, albeit in a certain fashion. This is a thing-mans game; running in doesn't get anything done. You have the research centre's AI, GLaDOS, Advising you, teaching you and occasionally cracking funny jokes, unknowingly. GLaDOS is well written, with a lot of character, and perhaps the best seen in any game, ever. GLaDOS also subtly changes, to a point and the change is well written in to subtly, and the change is natural and convincing (Slight spoiler there).
GLaDOS teaches you about all of the complexities of the portal mechanic (I was joking before) – Momentum, transportation of other objects, special awareness and more, as you go through test chambers. You get hold of the techniques quickly, as you have to; the game gets progressively harder.
There are also challenge rooms, which alter rooms for the singleplayer mode, so that you can get medals. Medals apply to all three categories: Time, least portals and least steps. Each requires a lot of thought and quick reflexes, but provides a great challenge if you've finished the singleplayer portion of Portal.
Test chamber 14
The test chamber design is reflective of the gameplay and story: It gets gradually harder and fits in with the story. That's the thing: The are no discrepancies with the story, level and gameplay design. As I said Crafted.
Each test chamber is only about getting form A to B, with various obstacles in the way, waiting for you to get around. Obstacles are interesting, and fit in with the setting, as they are original and fit the theme (which is consistent). Energy balls, acid, and more make interesting obstacles for you to circumnavigate.
Each is simplistic in design, usually a white tile room, with said obstacles in the middle, and a tunnel with an elevator at the end. The straight forward design is thrown up later on, using your expectations and knowledge of the test chambers to its advantage.
This next test is impossible
Running on the Half-life 2 source engine, the game looks good, without being great, and runs fine. It has a definitive look, and it keeps to it , and it is also something turned on its head later.