Hollow Knight is a metroidvania platformer, which are games similar to the original Metroid or Castlevania games, released February 24, 2017. It was developed by the three man company Team Cherry. Hollow Knight drops the player into their world with little to no context other than a short cutscene. Since the starting area is very linear with few areas to explore, most players should find their way to the first town very quickly. After this the game world opens up, but like most metroidvania games, many areas will be blocked off to the player at first due to lack of an ability or item.
At the start of the game, the player has 2 abilities one of which is called focus, it uses soul, which is a bar that can be filled up after attacking enemies and can be used to heal after a short period of time. The other ability is the nail, which is the players main attack throughout all of the game. The player can improve the nail ability by learning three new attacks, this can be done by visiting certain NPCs or getting pale ore by defeating some optional bosses.
Hollow Knight feature 35 bosses, most of which are optional, along with repeats of the same boss but with new abilities, defeating these bosses allows the player to collect upgrades. New abilities such as a double jump or items such as mask and soul fragments, which can boost the players health and soul bar. Theses bosses and items are scattered throughout the 19 areas in Hollow Knights world. Each area has its own unique enemies and some even change throughout the course of the game.
All of this content is for 15$,and is available on most platforms and can even be purchased for less when it goes on sale. A sequel to Hollow Knight called Hollow Knight: Silk Song which was also released recently, though as of publication it is only available on Steam. If you enjoy the game you should also check that out.