I'm not going to lie - these games don't last too long on my phone anymore.
I deleted 'Fibble' last week - I hadn't played it in months, and my daughters long ago stopped asking about it.
But 'Circadia' has some potential to stay a little longer.
I'll tell you why.
It's not plot-driven, as 'Fibble' was intended to be. (Though what that plot was I don't know if I ever figured out.)
It's more of a skill game.
There are a couple of levels of skill involved - using sight, sound, and, I guess, memory.
Here's what happens: There's a white circle somewhere on the screen. Then there are other circles (early in the game there are two - as you progress more come into play), and they emit these rings. The rings grow at different rates, and your goal is to get them to cross the white circle at the exact same time.
The rate at which the colored circles emit the rings is based on their tone - the deeper the color tone, the slower the rings come. (There's a corresponding audio tone as well.) So you have to work on the timing so that the rings approach the white circle at the same time.
Once you hit the white circle with all the rings at the same time, you advance to the next level. I imagine they keep adding colored circles, and there was even a level I played that had a moving white circle. But I've only advanced about 30 levels.
It's fun, and - good for me - not all that addictive. I can play it for just a few minutes to pass some time and put it aside pretty quickly.
Those are all elements that add up to a game that I don't expect to be deleting anytime soon.