Make no mistake: Portal 2 is a great game. I feel I would have gotten my money's worth if I'd just played it once because of the richness of writing and the plot development. And because the puzzles make you feel brilliant because they were so well-designed.
My first time through, I just played it as I wished. It took about eight hours because I wasn't racing to finish it. I firmly believe that your first playthrough should be instinctual — just play the way you feel is right.
But if you don't replay at a leisurely pace, in dissection mode, you're missing a huge amount of the game. Here are a few tips for making the most of your Portal 2 single-player experience.
1) Developer commentary
Replay each chapter in developer commentary mode (access it at the bottom of your menu when you start a new game), and you'll get lots of great info about plot points, technical decisions, and stuff that got left out of the final product. For the techies, you will get comments like this:
The dynamics you experience are computed as two nested, but actually separate, simulations. The first is a course simulation designed as a stress element analysis pass…There are over 300 rigid bodies and 900 constraints in this rig, all individually configured for properties like tensile, friction, and collision response.
If that's all gibberish to you, don't worry; you'll get plenty of other info that won't make your eyes glaze over. Portal 2 only contains 5% of the stuff the writers and devs at Valve came up with. A lot of the leftovers ended up in this mode. In fact, sometimes accessing a commentary bubble will actually take over the animation and let you see some of the subtle "facial" animations up close.
2) Stop and hear the roses
Here's a simple rule: If any character in Portal 2 tells you to "Hurry!" or "Run! Run! Run!"…don't do it.
I don't think there's any game that rewards you as much for just hanging around as Portal 2 does. Some of Wheatley's lines as he gets progressively more agitated ("Slight hint here: The button. Press it!") are far funnier than what you'd hear if you just complied immediately. In one place where he begs you to come back (and Chell would be stupid to come back), do it anyway. You'll be treated to Wheatley's best lines in the game.
3) Check out the Easter eggs
Signs on the wall, commentary about test conditions, semi-hidden doors, advertisements…it would be a sin to miss these added touches, especially because they come with even more great dialogue. And did you notice the 1970s-style Aperture logo?
4) Lines with new meaning
If you replay the game, you'll notice many "throwaway" lines of dialogue that suddenly acquire new meaning on a second playthrough. For example, the automated male voice in the first chapter refers to the ability of A.I. devices to survive on as little as 1.1 volts "in the unlikely event of a companion-cube-induced catastrophe." Brilliant.
Bottom line, you can have your cake and eat it, too, if you play Portal 2 the right way. And it'll be worth every second of your time.