I wish I could select multiple tags cause I feel like this one touches on all of them!
Serpentes is like the classic snake game you used to play on your Nokia phone, but with modern day design sensibilities. The game has this almost roguelike system in which each play reconfigures the way the reward progression works, and the more I played it, the more obsessed I got with finding the optimal way to utilize the rewards and get higher scores (which in turn unlock more starting "perks"). I lost a weekend of productivity to this game and don't regret a thing.
My high score was somewhere around 6,000 I think (I unlocked all the perks) and I had to force myself to put it down at that point. I'm also a big fan of the pricing model (you can play the full game for free, but a one-time payment of $2.50 lets you start with two perks instead of one for better scoring potential).