The difficulty, at least for me, is entirely in the controls. Normally, that wouldn't be a good thing, but it forms the entire basis of the challenge, forcing you to think quickly about what you're doing in order to navigate a 3D space. You're flying toward those walls at a high speed, and trying to rotate the block in three dimensions in time. Translating three-dimensional movement into presses of the d-pad and R button is as hard as it sounds. It is not intuitive at all, forcing you to practice before you can acquire the skill.
Or maybe that's just me. Maybe I have bad spatial skills. I can imagine the kind of person who rotates Tetris pieces in both directions, instead of hitting a single button over and over again every time, picking this up. I'm certain even those geniuses will find something to like here, as there are challenges beyond the basic fitting-in. Often, a hole will have heart-shaped items in it, which you collect by touching it with the block, further influencing your movements and giving you another rapid-fire decision to make. In addition, there are moving obstacles to deal with.
Oh, and you're timed. A timer counts down constantly, encouraging you to hold the L button to speed through each consecutive wall, and adding another layer of pressure.
A game very much like this one, also developed by accessory maker Keys Factory (baffling!), came out on WiiWare under the title ThruSpace, but it works better as a portable game. Not because it's divided into bite-sized challenges, though it is – simply because it's a lot more effort to put down a Wii game in a hurry and pick it back up when you've calmed down. You have to turn the TV back on and everything, instead of just opening the 3DS up again.
Ketzal's Corridors is available on the 3DS eShop for $6.99. We're always looking for new distractions. Want to submit your game for Portabliss consideration? You can reach us at portabliss aat joystiq dawt com.