This is one of my favorite games. I've installed a lot of mods for this off of Mod DB. I have completed this around 5 times. I use my controller and my keyboard and mouse. I prefer keyboard and mouse though. My fastest time is 1 hour. Now, I am a nerdy person and I LOVE THIS GAME! i have 3 achievements left. Which are for goals in maps for steps, portals, and time. At first the game is very hard, but after your first play through it's fairly easy. There are also bonus maps. Technically challenges. So there are the 6 challenge maps that are normal, but in each one there are 3 challenges. Steps, Portals, and Time. Some of those want you to use glitches. Each challenge also has bronze, silver, and gold. Of the 6 maps there are also more advanced versions for your enjoyment. Now for the plot. !NO SPOILERS! There is not really a plot. So you go through the puzzles as Chell. Now the only other characters are Turrets which are the ONLY enemies in the courses that die when they fall over. Also GLaDOS, She is the only character that talks a lot. So that's it because i'm not going to spoil it. This is the first of a series. Also the soundtrack is included for free.
Buy it from Steam for $10: http://store.steampowered.com/app/400/
I bought both games for $4.50 because they were sale
Also relased on: PS3, and Xbox 360
Official Website: http://www.thinkwithportals.com/. That is technically the second game's website, but still this is the website.