At its core, Portal 2 is a simple concept. Using a handheld device, you can shoot an orange and a blue portal that will instantly link any two points in space. Step through one portal and emerge from the other. That's it. Most of the time when playing Portal, you don't even need to worry about timing. You putter around, finessing the locations of your portals; then you move forward when you're good and ready. For players used to switching ammo types on the fly, zooming down a sniper scope for pinpoint accuracy, and running a split-second threat assessment on dozens of inbound hostiles, this should be kid stuff.
Instead, it breaks your brain.
Rather than using the portals to kill things, you mostly use them to navigate mazes. Those of you who've played the first Portal will understand the more advanced strategies. (Those of you who haven't should remedy that deficiency immediately.) Many puzzles are based upon conservation of momentum: if you can open a portal in the floor and jump through it from a great height, your falling speed will become forward velocity the instant you exit the portal you've placed on a wall. Others are simple logic puzzles. How can you direct a laser beam through a 90-degree turn?
This being a sequel, it is, by necessity, bigger, better, and more bad-ass, so the developers have thrown several new wrenches into the works. The game never lingers on any one feature. You'll make your way through a few puzzles that depend upon redirecting a tractor beam, and just when you think you've got it, you're switched to puzzles that depend upon a flubber-like blue gel to bounce you high in the air. Once Portal 2 realizes that you understand a puzzle mechanic, it won't repeat itself, except to thwart your expectations. Good luck figuring out how to get the blue gel inside the light beam.
Bigger isn't always better, of course, and it's fair to say that Portal 2 does lose something in the single-player campaign in the wake of its pared-down predecessor. Maybe the novelty is gone, but the cheeky robot narrators are less surprising this time, and the frantic chase scenes feel obligatory. None of the sequel's massive vistas and crumbling structures elicits the same frisson as your first step outside the test chambers in the first game. Even our beloved GLaDOS — well, I for one could have died a happy man without ever hearing her origin story. Still, Portal 2 could suffer only in comparison to Portal 1.
And if single-player Portal 2 is like Portal, only bigger, the introduction of cooperative play is where Portal 2 manages, once again, to surprise and delight. That it works at all is incredible enough. That the multi-player mode stands alongside the single-player in both duration and quality is a minor miracle. Not only are the maps even more confounding when you're dealing with four portals instead of two, but having a friendly face working alongside you takes the chill off the more hostile world of the single-player game. Solving a puzzle is even more satisfying when you and your teammate can do a celebratory dance.
To follow up a game as groundbreaking and as beloved as Portal must have been even more daunting than starting from scratch. Portal 2 shows that Valve's spirit of invention is very much alive and well.