While the rest of the world frets about the loss of Flappy Bird, some of us have become unexpectedly dependent upon a dazzling numerical puzzle game from Sirvo LLC called Threes.

I learned about the game through my friend Marco Arment, who gave a ringing endorsement of the game when he said it “doesn’t suck.” He’s right, in many, many ways. I was moved by his assessment to download and play the game. I’m glad I did, and I’m also devastated that I did.

It turns out Threes is a better game than I quite know how to comprehend. I want to play it again, and again, and again. It’s dangerous.

What is the secret sauce of Threes, and games like it? I’m not sure, but I have some impressions. If I were designing a game and I wanted to hope for anything near the irresistibility of Threes, these are the lessons I’d be taking from it:

1. It’s easy to learn. The game has a brilliant interactive training mode that guides you through the simple rules that govern the game. Even a game with simple rules will be put aside if it takes more than a minute or two to learn, so luring folks in with a tutorial is a good call.
2. It’s easy to “do well”. From the moment you start playing Threes you will find yourself making immediate, almost constant progress. The format of the game has smaller number tiles combining with one another from the very start, giving a fast-paced sense of progress that should thrill even novice players.
3. It’s much harder to “do really well”. Once you’re hooked, you’ll find yourself trying to figure out what it was about your choices in one game that made you do so much better than you did in another game. And if, like me, you’re not some kind of cosmic genius, you’ll be intrigued to figure out what that is. I’ve been balancing my play between “having a good time” and “struggling to understand.” Sometimes the two do overlap. I’ve developed some techniques that seem to be effective, but on the whole I recognize there is a lot of room to grow. There is a lot to understand.
4. It’s easy to get a reality check. Here’s a real kicker. If i were playing Threes in the privacy of my home without the benefit of Apple’s Game Center to let me know just how well my proud accomplishments stack up to friends and strangers, I’d be feeling pretty good. There’s even a chance that, without the knowledge of just how well other people are doing, I might reach a point where I convinced myself I had the game figured out. A quick glance at the high scores of my friends lets me know that I’ve figured out how to be relatively competent at the game (current high score: 9,132), but nowhere near as lucky and/or skilled as some friends and many strangers.

I’m sure these four points are the tip of the iceberg, but they are what stand out to me. Of course, it doesn’t hurt that the game is well-designed and adopts an honest business model (no ads or scammy upsells). The target audience for Threes is probably dramatically smaller than the audience of Flappy Bird, but especially for nerds or folks who just love a good numerical puzzle, Threes is a great value and an example of how great iOS games can be.