The main character is a girl with long dark hair in an orange suit, called Chell. Everything you'll find out about her comes from another main character, GLaDOS (Genetic Lifeform and Disk Operating System). GLaDOS will be the artificial intelligence that will help you to get through the nineteen levels of the game. Ellen McLain, an American opera singer, plays the voice of GLaDOS.
You may think that the game could be boring because it only has two main characters, but that would be a wrong assumption. Portal is one of the most innovative games in a long time. It is a real refreshment that the gaming scene needed after a bunch of graphically pumped non-imaginative games that have been released recently.
Your main goal in Portal is to get through the levels which get harder and harder as you advance using your Portal Gun. The Portal Gun is used to make a gate (portal) through which you or other objects can enter or get out. You have the possibility to make two different portals, a blue one and an orange one. One is used for entering, the other is used for getting out.
It is amazing that a seemingly simple game can be so fun and so hard at times. Sometimes you'll have to stop and think, you'll have to use your logic. Use boxes, balls, platforms and other objects to get to the next level. The physics engine is just awesome.
Every level in the game has to be studied and analyzed well before taking action. This game is like an IQ test, but more fun. The graphics are also very good and looks mostly like Half Life 2 because it's made using the Source Engine. Everything in this game seems perfect, from the physics, graphics to the original puzzles and good humor.
The only con of the game would be that it's gameplay time is pretty short. You'll be able to get through the nineteen level in less than four hours in you are an experienced gamer.
All in all, a very good job by Valve. I could write something else but that would spoil parts of the game, you just need to try this game out to see how fun it can be.