Furi is a new game that's free on PS+ this month. I'm not very good at describing things, so I'll just let some others do it for me. I'll just say it's basically a game that's only boss fights. Each boss has unique mechanics and multiple stages to the fight. I've only played the first two fights so far, but I'm loving it.

At the end of the day, it's free and it's a relatively small download (3.4 GB), so it's worth a shot. It's also available on Steam for $25 if you don't have a PS4.

From the developer's website:

Fight your way free in our frenzied all-boss fighter, and discover what’s waiting behind the last gate. Furi is all about the tension of one-on-one fights against deadly adversaries. It’s an intense, ultra-responsive game with a unique mix of fast-paced sword fighting and dual-stick shooting. Each of the formidable guardians —designed by Afro Samurai creator Takashi Okazaki— has a unique and surprising combat style that requires focus and skill to defeat. The high-energy action gets a boost from an explosive soundtrack composed by electro musicians Carpenter Brut, Danger, The Toxic Avenger, Lorn, Scattle, Waveshaper and Kn1ght.

And ACG's review (I really his reviews):