To do this, the team at Valve isn't simply crafting a bigger version of the original Portal. "That would be the opposite [of what we want to do]," says Johnson, explaining the length of the first was "about right" in "terms of different things the player was learning about." Instead, Valve is providing players with a number of new gameplay elements to learn about, something that will ideally add to the game's length but not its tedium.

Of course, the gameplay still revolves around portals--this is Portal 2, after all--with the bulk of the sequel's known additions enabling players to do more than just jump through these holes in space. For example, placing a portal near the opening of "Pneumatic Diversity Vent" enables players to take advantage of its airflow, meaning that those pesky sentry bots can be sucked through the portal, thus clearing the path ahead.

Another new addition, the "Aerial Faith Plate," vaults players (and other objects) high into the air. The "Excursion Funnel Tractor Beam," meanwhile, can be utilized with portals to push players and objects left, right, up or down--it all depends on the angle. And let's not forget about the "Thermal Discouragement Beam," essentially a laser beam that can be redirected through the use of portals and companion cubes to burn ...whatever.

But wait, there's more. Portal 2 also brings with it--thanks to Valve's hiring of the Tag: The Power of Paint team--two types of "gel." By using a portal to redirect the flow of this "gel," the surrounding area can be coated in a substance that either makes the applied area extremely bouncy ("Repulsion Gel") or extremely slick ("Propulsion Gel").

Combined with the gameplay mechanics of the original Portal--i.e. the importance of momentum--these new additions seem, at first, to be rather simple to wrap your head around. But when they all start to come together, when the puzzles start requiring these various elements to be used in conjunction, the possibilities are ...daunting.

Fortunately, Valve recognizes the dangers of making the game too difficult.

"The challenge for us is making sure that we do it where we're not making the game a lot more difficult or requires different skills than a Portal player generally has," Johnson notes. "We still want it to be where you think your way through a part in a level, you feel really smart when you solve it, and you have all the skills [you need]."

"What we're trying to do is, given that we have a lot more [in-game] time with the player this time around, we can introduce those elements at a proper pace, give the person enough time to master those, and then start challenging them and combining them."

In addition to single-player, Portal 2 also includes a separate campaign with puzzles designed around cooperative play. Unfortunately, I wasn't able to go hands-on with either mode, but tales of brain-twisting cooperative puzzles filled the convention center.

Toss in the trademark humor--the bits and pieces I saw were faithful to, and, dare I say, may have even improved upon the original in that regard--and Portal 2 is looking like a winner. Simply imagining what's possible with these new elements has me both excited and a bit terrified that I won't be able to figure them out, but I'm more than willing to take that risk whenever Valve deems it appropriate to release the game.

Developed by Valve Software, Portal 2 is scheduled to release simultaneously on PC, PlayStation 3, Xbox 360 and Mac sometime during 2011.

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