Hollow Knight is a hand-drawn 2D action-adventure that will have you face off against hordes upon hordes of monsters as you journey through a vast and interconnected world. Its not the most casual or welcoming game for new players, but there is enough depth and complexity present to greatly reward those that push through the initial difficulty curve.
All of that will soon be getting amplified as Hollow Knight is preparing to receive its very first and very tricky content pack "Hidden Dreams". The update will bring with it two new bosses to fight against, each of which with their own storylines and music tracks, the Dream Gate that allows you to instantly travel from one corner of the kingdom to another, as well as a brand new Stag Station to uncover.
The Hidden Dreams content will be accessible at any point in the game, whether you're starting fresh or already near the end. So while this update isn't bringing with it an expansion's worth of content, there will be enough present to occupy you for at least a few more hours as you get repeatedly slammed into the ground.
According to the most recent blog post Hidden Dreams will be coming on August 3rd as the developers still need to do a bit of tweaking before its ready. If you would like to grab Hollow Knight before the fact, or just learn a little bit more, I would recommend heading over to Steam.