Okami

Ōkami is a 2007 PS2 game (2006 in Japan), developed by Clover Studios, which sadly was closed down in 2006 after Atsushi Inaba, Hideki Kamiya and Shinji Mikami left the company.
They went on to found PlatinumGames, and made such games as Bayonetta and Nier:Automata.

The game is highly influenced by Japanese culture. Even the title itself is a bit of a pun in the Japanese language, although more so in the western releases, since it uses the roman alphabet.

The original title is written as 大神, which referrers to a major deity. The protagonist is Amaterasu, the sun-goddess; one of the most important deities in Shintoism.
Well, in this game Amaterasu is possessing the body of a wolf.
Ōkami written with the following kanji: 狼, means wolf.

The story and setting of the game is largely based on traditional Shinto myth and Japanese legends. Largely the Shinto record Kojiki, which is the oldest preserved Japanese book concerning Japans ancient history, and Nihongi.

Amaterasu emerging from the cave Ama-no-Iwato
(A famous story from the Kojiki)

The art style is based on traditional Japanese ink drawings and calligraphy.

The gameplay it self is very much what you would expect by an action adventure game in the spirit of such series' as Zelda.
You explore an open world with random enemy encounters, and interact with various npcs that offers help and sometimes side-quests.
The game is largely linear with main quests such as exploring dungeons and defeating bosses. But you are of course free to return to previously explored areas to find things you missed, or couldn't access earlier.
As you would expect from such games, you get progressively stronger, new weapons and skills becomes available and so on.

To not give to may spoilers the story is basically about a weakened Amaterasu-Ōmikami (The Shinto sun-goddess) inhabiting the body of a white wolf in order to revive a dead Nippon and defeat the evil eight-headed serpent Orochi (Yamata no Orochi in Kojiki and Nihongi).

Orochi as depicted in the game

What sets this game apart however, other than the graphics, settings, and story drawing so much inspiration from ancient Japan, is the use of "the heavenly brush".
This is an ability to draw on the world to create change. The screen pauses and becomes monochromatic to remind of a parchment and ink.
In the beginning you get abilities such as making trees and flowers bloom, and later on you can even turn night into day by drawing a sun in the sky.
These abilities are used to solve puzzles, and progress the story, as well as aid in battle.

The game may not be very rare, but many people I know seem to have been mostly unaware of it. This could of course be that they where put off by the unique style and inspirations that is so characteristic for the game.
For anyone who finds the artistic style appealing this is truly a treat.

I was lucky enough to get the game for PS2 when it was new for really cheap.
The game was later ported to the Wii which had much stronger colors, but apparently the controls where a bit more difficult (which I find rather strange; it would seem like the Wii remote would be perfect for the calligraphy interface).

It will get a HD release for PS4, XBox One and PC in December of this year (2017).

Both Wii and PS2 copies costs around €14-30