The puzzles in Portal rely heavily on Source’s innovative physics engine.
One of the dynamics you encounter is the use of momentum and gravity. Say there’s a ledge you need to get to, but is way out of reach. You can place a portal on the wall opposite of the ledge, and shoot another one down a shaft. When you jump down the shaft and into the portal, your momentum shoots you out of the destination gateway like a bullet and onto the ledge.
Some of the objects in the game are similar to what you’ve seen in Half-Life 2. There are no real “enemies” in the game, but there are gun turrets (similar to those seen in HL2), and energy orb receptacles. Several of the puzzles require that you get an energy orb from the source to its destination receptacle to open a door or proceed to the next part of the room. Since you can’t touch these balls of energy, you must paint a path with portals to get the orb where it needs to go.
The portals can also be used to eliminate your enemies. One of the game dynamics is to open a portal next to a gun turret, and then another directly in the path of a rocket launcher or orb canon, which causes the projectile to take out the obstacle.
There are other gameplay dynamics in the first half of the game in which you are running the experiment gauntlet that you must learn to complete the puzzles. These skills become absolutely crucial to your survival in the second half of the game, where you find yourself behind the test structure and must find your way out.
Didn’t I mention that? As you near the end of the experiment chambers (19 in all) you see evidence of your predacessors who have opened walls, written notes, or otherwise reveal the conspiracy of GLaDOS, such as graffiti stating “There is no cake.” Near the end of the experiment, your electronic overlord tells you that you will be “rewarded with cake” for your survival, and then states instead that “you will be baked” as a conveyor belt slowly lowers you into a pool of lava.
Using your portal gun, you can escape, and GLaDOS becomes very aggitated as you weed through the back rooms like an unwanted cockroach. She says things that will be familiar to anyone who’s dumped a psychopathic girlfriend, like “I didn’t mean it. I’m not angry, really. Just come back.”
The puzzles are no longer staged, but you must use what you’ve learned in the Enrichment Center to get past pools of toxic waste, lava, crushing platforms, and various turrets and obstacles. The puzzles become increasingly harder as you progress, but nothing too extremely difficult. You need to have good aim while you are flying through the air, as you will have to repeatedly fly through several portals to gain enough momentum to get out of some very high rooms.
Near the very end of the game you see the back offices of Aperture Science. There is an abandoned PowerPoint presentation in one of the offices that indicate that Aperture is in competition with Black Mesa (Gordon Freeman’s former employer) for government contracts. There are other subtle hints that give you a larger glimpse into the Half-Life world, which makes Portal more cohesive.
