The levels started of simple and easy, but as you progress through the game they seem to get exponentially more difficult. As I said before, I'm not really a big fan of puzzle games, but Portal just seemed to grab a hold of me and didn't let go until it was over. I started playing Portal as soon as it finished downloading and the mystery and obfuscation right from the start hooked me and pulled me right into it. I had heard of it over the years and always blew it off because it looked like a really poor idea for a game.
Though I'm not a big fan of puzzle games, (I usually tend to prefer the more violent games) I decided to buy the Portal bundle from the Steam Store. As an avid gamer, I pride myself on the diversity of games that I play.
