Disc-based video games, the ones that cost $60 and come in a plastic box, may be heading the way of the VHS cassette and the eight-track tape. Many industry pundits believe that by 2020, if not sooner, you'll download all your games -- just as you do now with music and smartphone apps.
Right now, though, the download-only market is still somewhat of a laboratory for game designers who want to experiment with new ideas. And no lab is wackier than the one you'll visit in "Quantum Conundrum" (Square Enix, X360/PS3/PC, $15).
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Kim Swift, the lead designer of "Quantum Conundrum," was the mastermind behind the 2007 classic "Portal," and fans of that puzzle game will feel right at home. Professor Fitz Quadwrangle has discovered a way to switch among four dimensions with unusual physics. The "fluffy" and "heavy" dimensions make objects, respectively, lighter and heavier; you can also slow down time or reverse gravity.
In each of the rooms in "Quantum Conundrum," your mission is to use your primary tool, the Interdimensional Shift Device, to escape. For example, you may need to put a safe on a pressure-sensitive plate -- but you have to make the safe fluffy to pick it up, then make it heavy to drop it on the target. By the final levels you'll be frantically juggling all four dimensions.
Quadwrangle, voiced by "Star Trek" veteran John de Lancie, is sarcastic but not quite as malevolent as "Portal" villain GLaDOS, and the jokes here aren't as sharp. But the puzzles themselves are every bit as clever.
"Spelunky" (Mossmouth, X360, $15) is one of the friendliest-looking games on Microsoft's Xbox Live Arcade, with an adorably stout hero who will remind you of a certain lovable plumber. But once you take a few steps into its mysterious mines, you'll realize this is one of the nastiest games ever created.
Each level is a two-dimensional maze filled with treasure, traps and monsters. Some traps will kill you outright; others will nibble away at your health.
It's fairly easy to survive the first few levels, but you will eventually die. And there are no saves or checkpoints in "Spelunky" -- every defeat sends you back to the very beginning.
Success in "Spelunky" requires playing each group of mazes over and over until you discover a way to tunnel through. The levels are randomly generated, so you don't see quite the same thing every time -- but after dozens of fruitless trips, they start to blur.
Deaths are frequent and cheap, and escape feels too often like a matter of luck. Some of the more hard-core gamers I know are raving about the unforgiving difficulty of "Spelunky," but I found it tedious and even somewhat mean-spirited.
Telltale Games' video-game adaptation of the zombie graphic-novel series "The Walking Dead" (X360/PS3/PC, $5 per episode) has been much more compelling than the AMC series based on the same material.
Episode two, "Starved for Help," finds the survivors holed up in a motel and running out of food -- but when aid arrives, you have to make some tough decisions about whom to trust.
"The Walking Dead" isn't a zombie shooting gallery like "Dead Island" or "Left 4 Dead."
Instead, it's a thoughtfully paced drama in which the still living humans can be just as dangerous as the undead ones, and every act of violence is surrounded by ambiguous moral choices. With three episodes still to come, I'm dying to find out where these characters end up, which is more than I can say about the stiffs on the TV show.