Bleach. The series is long (over 300 episodes) and as a result this review will cover the earlier part of the series. The major premise of Bleach is the adventures of high school student Ichigo Kurosaki after he becomes a Shinigami and begins defending his friends from evil ghosts.
Ichigo Kurosaki is a high school student who can see ghosts, one night he encounters Rukia Kuchiki, a Shinigami hunting an evil ghost known as a Hollow. He becomes involved in her battle and ends up being given her powers. As a result Ichigo takes over her responsibilities as a Shinigami, primarily defeating Hollows who attempt to kill humans. The series follows his battles as he protects his friends and family and interacts with other participants in the world of spirits.
The series features a lot of the combat that would be expected of a shounen series filled with swords and monsters. The main appeal of the series is a mix of the passion the main character fights with and the massive number of unique abilities that show up in the series. The main weakness of the series is poorly placed filler arcs which occur in the middle of one arc due to the show catching up with the source manga. Beyond this the series is consistently good with a large cast of interconnected characters and plenty of stirring scenes.
I'd recommend this series to anyone looking for something to watch casually over time or is a fan of other long shounen anime like One Piece but looking for something a bit more serious.