Fantastic game with pixel graphics. In short, you came to the Gungeon to kill your past because you are ashamed of it. But the path is rather difficult - you will have to traverse through 5 dangerous floors, (and if you wish to, you can go through 5 additional secret floors) as well as collect the pieces for the Bullet That Can Kill The Past. Every floor has its own unique boss, and sometimes their attacks can be random, so you'll have to be careful.
Main features of the game:
- awesome soundtrack
- five main floors + five secret ones
- excellent spritework
- unique gameplay
- difficult bosses
- four main characters + four secret ones
- tricky achievements
and much more...

I highly recommend you try out this game.