Grimstorm is hard. Really, really, really hard. It's free, too, which definitely balances out some of the pain of how horribly hard it is. But not much.
You play a knight assaulting an ancient, foreboding castle filled with evil guards and imposing bosses. You're armed with a sword and shield, the former you can swing with a tap of the space bar and the latter is raised by holding the down arrow.
Attacking enemies head on will see you be cut to shribbons; instead you have to watch the animation of enemies and learn their patterns to succeed. The guards, for instance, will only attack you when your shield is down so you have to stand unguarded until they swing. The moment you see the animation begin you need to switch stance, block the hit, and then counter-swing before they duck behind their own shield.
Death sends you back to the beginning of the castle and respawns all your enemies but any doors you've unlocked stay open so, with persistence, you can unlock shortcuts to the bosses without losing all your health on the way.