If you want the short review, here it is: Stop reading right now and go download the Aquaria demo now! (Windows, Mac)
Aquaria is an independently developed adventure game for Windows, Mac, iPad and Linux. You play as Naija, a young undersea dweller who does not know who she is or whether she is the last of her kind and sets out to find answers. Little bits of the intriguing story are revealed here and there, but most of it comes at the end. Even then, the ending (especially the full ending for those that find all of Naija's lost memories) seems to leave the player with more questions than answers. Perhaps a sequel will elaborate.
Some things set this game apart from others produced today. Probably most notable is the fact that Aquaria is a 2D game. Not in the 8-bit pixellated old-school graphics way, but in the “you move up, down, left and right” sort of way. The gaming world has become so fixed on 3D that it tends to forget the possibilities of 2D entirely these days.
Secondly, Aquaria is freakin' gorgeous. The graphics are beautifully hand-crafted, giving the whole game a painterly feel. Check out the screenshots and videos at their web site to see what I mean. The visuals by themselves make the game world worth exploring.
That brings up another thing: The game world is enormous. You would expect a game that was basically put together by two guys would not be nearly so expansive. Even in the demo, the world is large enough to give you a good two hours worth of exploration and gameplay. (With most demos, you're lucky to get half an hour.) A big part of the game is exploration, discovering new areas and finding new things to see and do. In this sense, it is similar to the Metroid games.
Sometimes you'll get new abilities, which may allow you to reach areas that were not available to you before (swimming against strong currents, opening doors, finding your way through the dark, etc.). Because of this, there will be some backtracking involved. That isn't for everybody, I know, but the great scenery makes it worth it, and the game does provide a mechanism for moving rapidly to other parts of the world.
Another remarkable thing about the game is the great voice acting. Voice acting tends to be hit-and-miss; even major gaming studios put out games with mediocre voice acting. Not so with Aquaria: Naija's voice perfectly complements the game. Naija is voiced by Jenna Sharpe, and she does a great job of lending some real emotion to the character.
A nice thing about the game is that it isn't chock-full of violence like many games today. Yes, there is combat in the game, including boss characters, but it is handled far more tastefully than seems to be typical in mainstream games these days. There are some genuinely creepy parts to the game, so I wouldn't go so far as to let very young kids play it without being there with them, but if it were rated by the ESRB, I would imagine that it would net an E10+ rating.
Probably most compelling for me was the level of craftsmanship that is apparent in the game. For example, you will often encounter areas of the game with creatures, plant life or other elements that serve no purpose in the game plot-wise, and that appear nowhere else in the game. They just serve to make each place unique and to give little rewards to the player for exploring. You just don't find that level of craftsmanship in most games; they just don't “waste” much time on that sort of thing. It's a shame, since little touches like that are a great benefit to games, especially ones which focus a lot on exploration.
I highly recommend Aquaria. Really. Go get it.