Bullet hell is a game where enemies fill the screen with hundreds of projectiles arranged in intricate patterns, and you have to slip between them. At first, it seems impossible, but gradually you begin to see the patterns and dodge almost intuitively. The genre originated in Japanese arcade shooters and is now found in roguelikes and action games.
Usually yes, but many games have difficulty levels and training modes. A milder version of the genre is "Bullet Paradise ," where bullets mostly come from your gun.
You can download bullet hell games via torrent: the filters above will help you choose by language, size, and build type.