I've had an idea for a game for a while that I've been wanting to explore, and this game jam could be the perfect opportunity to do something with it. However, I'm wondering if it really fits the Metroidvania genre well enough to be eligible.

It would be a game about exploration of a 2D map, with areas that are unlocked over time and upgrades to the player's skill set making backtracking worthwhile to uncover secrets. However, the focus would lie heavily on puzzles and a rich narrative. There wouldn't be fast-paced action, platforming or battling enemies in the traditional sense. It would have a more slow-paced, laid-back feel to it.

Does this sound like it fits the genre well enough?

The core is there: exploration and unlockability. Everything else is a nice twist on the genre. You have my vote!

As long as you have non-linear exploration and unlocking of abilities that not only allow you to progress but also have gameplay usability, it should fit nicely into the metroidvania definition.