5. Portal 2
As I mentioned earlier in this series, you'd be hard pressed to find any gamer who'd disagree that Portal is one of the greatest and most important video games ever made. A sequel was, thus, a very risky undertaking, but I don't think anybody doubted that Valve would deliver, and they absolutely did.
Portal is iconic for subverting the player's expectations at what they believe to be the end of the game, the big reveal being that it's actually the halfway point, and that you then must step behind the curtain to make it through the second half of the game. Portal 2 kind of succeeds in pulling this off again, finding a new way to throw you behind the scenes.
You begin by waking up in a dilapidated version of the Aperture Science facility that you knew, having been in stasis for an indeterminate amount of time. You begin getting guidance from a friendly little ball named Wheatley (voiced brilliantly by Stephen Merchant), who guides you through the broken-down testing chambers through to the central control area so that you may rendezvous with your old friend GLaDOS.
A turn of events suddenly sends you and your archnemesis tumbling down a long shaft, into the belly of the abandoned salt mine upon which the facility was constructed many years ago by eccentric bizarreionare (I just invented that word!!!) Cave Johnson. That's the only bit of backstory that you're spoonfed, but if you take the time to look around the rooms that you encounter, you can learn more about Aperture Science's origins.
There wouldn't be much point in a sequel without introducing some new mechanics, of course! There's a reversible beam that will carry you across dangerous pits and in and out of portals at its end. There's a light bridge that can be sent through portals. And there's gel! Three colors of it, in fact, all of which do different things, leading to some fantastic puzzles that make you lay out the various goops in ways that allow them to play off of each other.
Portal 2 is an absolute slam dunk. If you loved the first one (and I don't know how you possibly could not), you will love this one too. I would eventually love to see these characters in a third installment of this story, but I'm glad that Valve takes their time with this series, because the puzzle mechanics themselves lead to infinite room possibilities, and in the hands of a lesser developer that would no doubt have led to a series of shovelware Portal titles. That shows how much they care about and respect this series.
I must also mention the co-op story mode, which is as fantastic as the single-player campaign. Grab a friend and play through it!
