First off, if you are reading this, haven't beaten the game and intend to... STOP!! I will be talking about the ending because I found it highly amusing, and I do not want to ruin it for you <3 If you have finished it, or spoilers do not matter to you, read on friends!
So first off, the game itself was AMAZING! I loved it. I liked how it was run, as though you'd been locked away for who knows how long, and you are trying to break out with a little robotic companion, Wheatley. His a friendly robot, with a funny British accent,and is generally helpful. Well, until he has you plug him into an electrical mainframe and you accidentally wake-up GlaDos again. Yeah... No Bueno.
So, as she's waking up, she reveals to Wheatley that you are the human
he's been talking about that defeated her, and she then promptly picks him up, and squishes him. She helps you find the dual portal gun, and now it's back to testing in her sick and twisted games again.
A few test chambers later, Wheatley reappears apparently restored to his former working condition and perfectly fine. He's trying to find a way out so you can both escape or replace GlaDos before she kills you. One thing leads to another, he replaces GlaDos, she gets put into a Potato:
As you go through the test chambers, you reach the 1960s version of Aperture, and more Recordings from Cave Johnson. You also hear his assistant, Caroline, who's voice seems to trigger strange responses from GlaDos. But more on that later.
Once you get to the 1970s version of Aperture, Cave Johnson is dying from exposure to moon rocks, which you have to use in the following chambers to get through. This is where my favorite Cave Johnson Recording comes in:
I still get the giggles every time I listen to this. So anyway, soon after this, you get out and are back to the main area of Aperture that we the players know and love. Wheatley has of coarse taken over, and he's not very good at making test chambers.
The longer he's in control the more things fall apart. Most importantly, all of us nerdy people should get a kick out of this eventually sight at the start and end of each chamber.
FINAL BATTLE NOTES AFTER THIS POINT! This is your last chance to turn back!!
So GlaDos brings you back to the circuit room that took you to her room in the first place. You plug her in, she send you up. Wheatley is waiting for you, and lets you know that now you will die. He watched the videos of you killing GlaDos originally, so he turns on the neuro-toxin right away, and uses shields, that are not really effective. He launches bombs at you, you use portals to launch them at him around the shields he's using. GlaDos periodically sends you corrupted cores to attach to him. Eventually, you get him to 100% corrupted. You try to press the stalemate override button, and he uses a booby-trap to blow you back away from it. The top of the room gives way, revealing the moon. Launch a Portal at it you say? Of Coarse! So you do, and Wheatley, you and the cores get sucked out. Wheatley is held on by a single cord, which GlaDos cuts, which launches Wheatley into space since you are on the moon. GlaDos pulls you back in and you black out.
Once you wake up, GlaDos informs you of her being your savior because she was originally a computer clone of Caroline, but she's morphed into something else, so she deletes Carolines files. Carolines memories and emotions are what made her save you in the first place. She promised to let you live though, so she allows you to go to the surface. As you ride up you get to see a turret orchestra, and finally, Earth. Best part of all, is what follows you up at the end:
(I may have squeed a little. I love the companion cube <3... and remember, it will never threaten to stab you )