I have a basic idea that I think would make a good simple puzzle game. I've seen it in a number of other games as a mini-puzzle so I'm sure it's very familiar (and already a really well known title somewhere which for some reason I can't remember), but it should make a good practice game.

The idea is a vaguely maze-like puzzle game set on a frozen patch of ice. The player has to navigate their avatar from point A to point B. However due to the frictionless surface of the ice the avatar can only change direction once they hit an obstacle. Thus the playing field becomes a kind of maze without walls; the challenge is to find the correct sequence of moves to get to the desired location.

Yup, pretty simple, and I'm sure you've all played in countless times in other games (I remember a puzzle like this back in Ultima Underworld, and I'm sure there's some earlier examples). However it should make a decent little puzzle game that I could quickly implement as an "ice-breaker" back into game development. I can spend a bit of time making a decent in-game level generator, maybe adding a few extra gameplay features and making the art all spiffy.

Then once I've got my feet wet and the engine ideas all sorted, I can make a more complex game for Iteration 2 with a higher chance of success.