In one game, it's an easy and somewhat frustrating platformer based around platforms that disappear and reappear on timers. It looks really cool and dynamic, for what's essentially the block timers from Mega Man 2, but instead of just disappearing, they fade into the background. The platforms are color coded, and when the background's color changes, the corresponding blocks disappear, coming back when it shifts to another color.
Alternately, it's lights on tracks or timers that reveal certain platforms or pass over them, or enemy shields that follow the same rules. The idea is basically that the same color cancels itself out. It's a cool idea that's not used in a particularly interesting way. It's just timers you're jumping around, not for puzzles or anything in particular. This is a concession to the second game that this is, and more on that in a bit.
As a single player game, it's very simple and orderly, a low stakes platforming game that still sees fit to mock you after every death, whether it be a mistimed jump, or because you got caught up on the side of a wall thanks to the sometimes spotty collision detection. I never felt much going through this way, except annoyance at how long it took to restart the levels. I don't mind dying, but it goes through a screen that's got messages akin to when you jump in the water in like a Tony Hawk game ('all washed up!') before dropping you in, counting down from 3, then letting you go again. I sure do love waiting!
The second is an overly chaotic multiplayer mode basically based around being a dick to other players as you race through the same platformer levels. With up to 9 people. All crammed onto the same screen, trying to get to the same location, able to pick up power ups and punch each other while desperately attempting to make it from point A to point B the fastest. It's uh... it's nonsense.
But unlike similar "this is far too many people and what's even happening" type games like Super Smash Bros, since this one has a goal you need to complete before you can go on, and is a little more skill based and less based around just smashing things and laughing as it all goes crazy, that means there's more room for it to fail and you're having to redo levels, spending more time trying to somehow wrangle 9 people into reaching a goal when that's hard to do even with 4 people.
I wasn't able to play Runbow with 9 people, though, so maybe I'm wrong. In fact you might have a wonderful group of friends who you play games with who are sitting around and lamenting that your odd-numbered group of 9 people can't play a game together and someone's always left out and if only you could you'd all be on the same team and do everything together, even as you cajoled for first place. Maybe you do exist somewhere out there in the world and not just in the hypotheticals of this review.
But it's not going to be too long before it becomes clear that one or two of you are really good at this game, and since it's not based around the kind of rubber-banding that drives competition in Mario Kart or something, they'll just take it away. Soon it wouldn't be a surprise for you to hear them grumbling and wanting to return to Smash instead.
Though you can also play online, but my attempts at this didn't really have a huge success rate for getting other people in.
While the inclusion of a 9 person multiplayer is indeed intriguing, there just isn't enough to Runbow to really make you along want to come back, let alone the 8 other people you can possibly finagle. It's simplistic jumping on levels for time trials, or it's overly-chaotic racing around the same platforming levels. It's not like the WiiU is hurting for good 2D platformers that you can play instead.