Took me less than 60 seconds. I'd say it's a perfect little puzzle. Next one you encounter you know the rules.

I'd argue 2048 is harder to learn and that was a popular game.

I actually thought 60 seconds was a bit too long. An easy to understand puzzle is probably more intuitive and < 15-20 secs from start/enough not to notice it took time.

It's a puzzle for people with a CS degree. You need to recognize state transitions and conditions. Other people will take much longer.