Aquaria is an inde game about a Madja, a girl whose lost her memories, expect Nadja isn't a human, she's an underwater humanoid...
Calling it an underwater Metroidvania combined with Ecco the Dolphin would be entirely accurate...
The game is about exploring, finding new powers that will help you reach the next, lather rinse, repeat. But like a good "metroidvania" it works and it's fun to play, in the beginning it's almost soothing to swing amongst harmless fish but as you'll progress you have to spend more and more time fighting and dodging.
You'd think it would monotonous being all underwater, but the variety in enemies and areas is big enough to not let yourself get bored! The game is filled with secrets, some are just for fun and some make the game a little easier.
One of the thing I liked about the game is the cooking system, it was quite satisfying to combine items and create a new recipe all by yourself!
It's about the average length of one of these kind of games, 10-20 hours depending on whether you want to get everything or not, and the difficulty escalates to an extremely high point near the end, but I most heartly recommend this game!
30$ for an indie game might seem much, but you can always try the demo to see if you'll like it or not! :3