Well, Nitrome is here for you.
Onekey is a character-based platform game played with only "one key", and thus the mystery of the title is solved. The [Space Bar] is your one and only method of control, and if your space bar is anything like mine, it's quite a bit larger than the other keys, and you can probably find it by feel if your attention happens to be on something else, like cookies. Or fireworks. Convenient!
The game, set in a colorful Mayan fantasy land, concerns a rite of passage. Your hero is a little Domo-Kun-shaped fellow with a warpaint mask and a tribal bone decoration in his face. Where he got the bone is a mystery, because on his own, he has all the survival skills of a roll of tape. He probably ambushed a bucket of fried chicken and kept the bones as battle trophies, and now all his friends are snickering at him behind his back and calling him "Hunts-With-Spork". Your job is to shepherd him through 20 levels worth of pitfalls, traps, and stonework guardians, using only the power of your Mighty Space Bar.
The catch is that you can't affect the main character directly. Instead, you control various objects in the environment while he blunders around falling off of things. If you want him to jump, for example, you have to wait for him to cross over a launching device and then hit space to catapult him into the air. Hammering on the space bar repeatedly raises gates, and keeping it pressed down moves certain platforms. You're like the spirit of the ancient ruins who, despite the fact that you're bristling with death-traps, would like to avoid maiming the local tribesmen. The tricky part is that you can't pick and choose what you manipulate. The Mighty Space Bar operates everything at once, including all the enemies, and stuff like arrow traps and crushing ceilings. You have to constantly judge the threats against each other, and think quickly, because your helpless charge—as though driven by pure stupidity—will be on a relentless quest to impale himself on sharp wooden stakes.
Analysis: This is a good one. The streamlined interface seems to have inspired the Nitrome team to create a wide variety of obstacles that interact in engaging ways. This is what you might call "fully exploring the concept." You'll encounter just about every possible combination of bad guy, trap, and moving platform during your 20-level adventure, without a lot of wasted design space. Since you only have to worry about one control option, the emphasis is always on timing and forethought. New objects requiring new strategies appear at a constant rate, and overall, I think Onekey is a little less punishingly difficult than the average Nitrome offering.
If you're hungry for a greater challenge, however, you can try to collect all 5 gems in each area, so little Hunts-With-Spork can afford to buy another bucket of KFC. No, seriously, the collectibles are pretty useless as usual, but they somehow feel more significant here than in other Nitrome games, because you have to take very specific actions to reach them. They aren't just sitting around in every spare corner. In fact, this seems like a step forward for Nitrome's level design. It's relatively easy to make it through the levels intact, but taking the best path just about triples the difficulty. To my way of thinking, that's more or less how it should be.
Oh, and Onekey is very, very pretty, if maybe a little desaturated. The Mayan theme suits Nitrome's tendency toward squarish, bulky visuals, right down to the angular background vegetation. The main character feels solid and three-dimensional, and the adorable bouncing feather on his head gives you something hypnotic to focus on while you poise yourself for the next bout of precision space bar mashing. The music doesn't exactly fit the theme, but it does match the bouncing of the feather pretty well, and I personally never felt like turning it off.
The one real argument I have is with the pacing. When you're in the midst of the fray, trying to manage spinning fans, rotating blocks, and leaping fish sculptures all at the same time, you'll be grateful that your hero walks like he's taking a leisurely stroll through the local vegetable mart. But when he wanders off to the edge of a long, uneventful platform and back, you might wish he had a "run" or even a "jog" setting. He's stuck on "mosey", and the downtime this causes can bring you perilously close to remembering that you have bills to pay and a cat to feed.
But I have to hand it to Nitrome for their likable character design. When a game's protagonist is this dumb, there's a very real danger that you'll lose sympathy for him. As in, "Please don't walk off that cliff again, you fat-headed plank, or I'll burn your family." But I don't feel like Hunts-With-Spork really deserves my ire. He's too oblong to hate. His resume lists his special skills as "making an oo-face" and "tottering". He's like a jaunty, devil-may-care, feather-sportin' sofa cushion. All he wants out of life is to roast a pig with his mates and perhaps not be squashed by a giant stone block. And you can make his dreams come true, all for the price of a broken space bar. You lucky benevolent deity, you.
Thanks to the millions of you, too many to name, that sent this one in. =)