The easiest way to describe 5th Cell's Run Roo Run [$.99 / HD] is to call it Canabalt, but with levels. That works. In the game, you control a kangaroo in search of its joey, and the path to finding it involves plenty auto-running and manually hurdling obstacles. To jump, you tap the screen. To run, you tap the screen. It's as much of a triumph in that style of minimalist design as Canabalt is, and it has similar elements and mechanics.
The "but with levels part" is a pretty big game-defining departure. Run Roo Run's world has oodles of color and instance-based content. In all, it rocks over 400 levels, all of which are clumped into individual chapters that introduce new mechanics. You'll bounce on tires, float on fans, play around with a double jump, and avoid retracting spikes as well as the rest of its outback's hazards, like cactuses, jagged trees and wood, and so forth. The way the game builds on itself, considering it has just a single, super-easy action, is pretty impressive.
Most levels break down like this: on a horizontal plane, you'll be presented with two or three jumps, all with repercussions for failure. Jump too soon, and you might hit a wall or a jagged rock. Jump too early, and you'll collide with the obstacle. As you progress, you'll be jumping to a tire, bouncing off of it at the perfect moment into a double jump that'll carry you in-between two rocks and to the level's end point.
Each level is designed to be super breezy. You'll finish most 3-5 seconds. You'll then be graded and awarded a medal based on some sort of behind-the-scenes magic, presumably tied to the amount of jumps and time spent.
There's a level of thoughtfulness, precision, and attention to specific points of design throughout the game. The jumping mechanic has no give -- when you jump, you've committed; you can't make adjustments. Since this is the case, consideration of how you're going to do something is integral, and so is your observation of level structure and your callbacks on how to do stuff.
Being tuned for scrutiny isn't a problem, by the way. Even though this is a particularly bloated game on an art production level, 5th Cell holds back on filler. Every piece of a level has a purpose, and it's that purity that helps you understand the hazards.
If you wanted to be crazy about this, you could probably call Run Roo Run a "masocore" game. Like a Super Meat Boy, or even Run Roo Run's inspirational material Space is Key, Run Roo Run is all about the thrill of perfectly nailing an increasingly convoluted set of actions in rapid succession. The reward is your accomplishment -- the platformer equivalent of a puzzle game's "a-ha!" moment.
I think the key difference here, though, is that this game doesn't hate you. Every time you jump, 5th Cell throws an arrow on the floor. This helps you focus on that third jump, as you'll be able to easily gauge where to jump again on the first two based on the arrow. Additionally, you can buy or earn level-skips and a fancy bullet-time aid that slows the action down. The in-app purchase stuff, by the way, doesn't interfere with the game.
More importantly, though, it just doesn't set you up for failure like most of these masocore games do. The action is straightforward; each jump is mightily choreographed, each obstacle plainly displayed. You'll never be left scratching your head or feverishly thinking about what your iPhone would look like with its gears and guts sprawled gushing from the sides.
Undoubtedly, 5th Cell is going to get some flack because the overall game is tuned to be easier than it could be -- the vast majority of its hundreds of levels are these simple, breezy romps. There are "Extreme" offerings, however. After finishing a chapter, you can go back and compete in a series of a dozen or super challenging levels. I don't mind the casual build to a remarkable level, so the difficulty isn't a problem for me.
One neat point: 5th Cell is apparently going to get behind Run Roo Run in a big way, as it'll be uploading 10 new levels a week beyond release. It's unclear how long it'll keep this up, or really what base this will serve, but it's a neat idea.
I think you should check this out. Run Roo Run isn't the most original game ever, but it takes the best out of a lot of worlds, and then owns that stuff. Its entertaining in big or small chunks, and those challenge levels are a whole new world of hurt. Give it a shot.