Hollow Knight will receive an update with two new bosses in July

While I still haven't played it, it is certainly one of the better -- if not one of the best -- indie metroidvanias out there (and there are many). Happy to hear about the update, and it's free too :)

Info straight from Steam:

• 2 New Bosses - Leap into battle with the mightiest foes! These epic new duels will test even the most skilled of players. Each fight grants rewards to the victor, though note: Engaging with each imposing boss is entirely optional! Who are these enigmatic, impossible-to-discern figures? We’re not telling! It’s up to you to find out this July!
   
• 2 New Tracks - Epic battles need epic music and Chris’s been preparing just that, with stirring new boss themes for each encounter! He's gone all out on these ones!
   
• New Upgrade: Dream Gate - Discover a whole new method of traversing Hallownest! Slice through the Veil and travel in an instant from one corner of the kingdom to another.
   
• A New Stag Station Uncovered - Hallownest’s stags once travelled the breadth of the kingdom, but with the departure of the King, one station was walled away, hidden from bugs and forgotten by stags, until now!