So I'm gonna talk about Portal.
I think Portal and Portal 2 were both amazing games. The story line was good for both, as well as the gameplay. The idea of a portal gun and solving puzzles with it was a genius idea, and it was executed perfectly. The puzzles themselves take some thinking, but aren't so difficult that it makes people give up.
Now onto other aspects of the game. Mainly Glados, voiced by Ellen McLain. She is one heck of a voice actor, and also is a good singer. She portrays Glados perfectly, and is very smooth. Glados the character is probably the #1 Video Game Villian in my eyes, although at the end she does let you go, which btw was an extremely satisfying ending if you ask me.
Last thing the plot twist in both Portal 1 and Portal 2 were surprising, and well done. Unsuspecting players in Portal 1 were extremely surprised when Glados tries to kill you, and you probably failed to escape the death trap the first time (I did). As for Portal 2, Wheatly taking over was PERFECT, because he was trying to help you, but got power hungry. Neither one I saw coming, which is what I loved about it.
To sum up, Portal 10/10 would play again for a long time and Portal 2 11/10 would play forever.