Portal 2 is the quintessential sequel that fans of the original have been waiting for.
When Portal 2 was originally announced to be a full priced retail game that would include multiplayer, I, like many others, was skeptical. After all, we've seen lots of games (BioShock 2 comes to mind) tack on a multiplayer mode just to try to appeal to the fact that multiplayer sells in this era of gaming. Luckily, Portal 2 isn't just something Valve put together for money or casual interest with a shoddy multiplayer component. Portal 2 is fully worth it's price for being an example of perfection in game design, with wonderful pacing, thought-provoking puzzles, brilliant relationship-testing co-op, and amazing humor that outdoes the original.
The writing for the game is primarily a reason why it is simply one of the funniest video games I have had the pleasure of playing. It also helps that the voice acting cast is fantastic and the level of dialogue the player hears just happens more often than in the original Portal. It's not as quiet of a game, and it's not as dry in it's form of humor, but the tone and ability of Valve not having to take it seriously is part of the reason why it's laugh out loud funny. GLaDOS is surely at her best in Portal 2, but the new characters like Wheatley and Cave Johnson are fresh and all work together to make the game as entertaining to watch as it is to play.
One of the reasons the gameplay of the original Portal was so appealing was simply that it was hard to fathom another human being coming up with these puzzles. Portal 2 may not come off as challenging to people who played lots of the original, but that will only be because the original conditioned your mind to understanding how the game works, and that alone is the mark of brilliant game design. What Portal 2 does however, is add tons of elements to the gameplay that vary it so that everything the player encounters is constantly fresh. It's not so much agility-based puzzles with tricky Portal jumping, but more of a patient analyzing process of the room and experimentation with what the test chamber gives you so that you can figure out what to do. Some purists may not like it, but I loved the new approach. There is an unbelievable level of creativity in the thought process that went into some of the puzzles. Unraveling how it all works is an indescribable kind of fun.
Portal 2 sets the bar for a sequel in 2011, a year where the majority of hyped releases are second and third entries of a franchise. It will be very difficult for most games to come close to this quality in the year but I look forward to seeing how Valve's amazing talent will push other developers to try and compete.