The big winner at this year's Independent Games Festival, Aquaria is a two-dimensional underwater action-adventure that puts you in the scales of Naija, a little mercreature who suddenly wants to know about the world around her and the origin of her species, and sets out to explore.
This you help her do by clicking around the screen to move, and using a wheel of musical icons activated by holding down the right mouse button to activate special abilities. Rather than an enormous, shapeless ocean playground or a flat sea floor, Naija's world is a network of tunnels and caverns full of fearsome fish and cranky crustaceans and puzzles that the abovementioned abilities help her to overcome.
The result is something like an underwater Castlevania, with shades of a 2D space shoot-'em-up. You feel your way around a well-populated and beautifully hand-painted world until you come up against the boundaries of each area, and by applying things you've learned and acquired you're gradually able to penetrate further. You learn the rock-moving spell to unblock passages around your home; you learn to project light so you can explore an abyss; you learn to activate pearly switches so you can kill a giant underwater lion. Fish. Thing.