In case you think my enthusiasm for the series is slightly overdone, I will point out that the sequel is not perfect. Load times are, quite frankly, hugely frustrating. Every time you beat a room, the game takes some time and loads up the next one. That's all well and good when it's taken you a whole long time to figure out how to proceed in the last room, but when you blaze through the room and are itching for the next only to get slowed by yet another load it's becomes discouraging.
Are load times too high a price to pay? No, unquestionably not. Portal 2 is a great expansion of the franchise and manages to successfully bring in new players without overly dumbing down the start of the game for experienced Aperture Science Handheld Portal Device users.
One more word of caution, Portal 2 is a huge time suck. The sense of accomplishment you get when beating a puzzle will cause you on more than one occasion to utter those famous last words, "just one more and then I'll be done." You'll end up beating the game in a minimal amount of time that way (it is a longer campaign than the last one), but the rest of the world may fall by the wayside for a little while. You won't regret your choice to continue, but those around you may get frustrated.
Portal 2 is rated E10+ (Everyone 10 and older) by the ESRB for Fantasy Violence and Mild Language. This game can also be found on: PC, Xbox 360, and Mac.