It's ridiculous how almost every game that packs a challenge is somehow connected to Dark Souls. Take a step back: Dark Souls was hard because it offered limited speed and encouraged clever approaches when entering new areas and fighting enemies.
Cuphead is nothing like that. At its core, Cuphead feels like Contra with 1930s cartoon aesthetics. It's a bullet-hell experience where every single thing is out to get you. Almost every stage you visit has an epic boss fight with several phases. The non-boss stages, which are rare, are filled with enemies programmed to crush you every step of the way.
It does get frustrating. This isn't Dark Souls where once you've been surprised once, you can do better next time. Cuphead challenges you by being more random. Sometimes the randomness is sporadic and subtle, such as an enemy spawning in a spot where it shouldn't be.
The bosses are less random from what I can tell, as attack patterns change every so often. You might fight a unicorn centaur who fires lightning bolts or you might fight two sisters dancing on clouds who throw damaging tiger-look glances.
The boss fights themselves are not long. My average time taking down a boss is less than three-minutes. But it will feel much longer considering projectiles fill up the screen really fast. You will find yourself dodging at least five different things all at once while platforming to look for their weak spots. The release once you defeat a boss is always cathartic, but it is also exhaustive; especially if you've fought the boss multiple times in a row.
Much of the reason why the game is hard stems from the absence of checkpoints. In long, drawn out levels, you feel safe and secure as long as you hit a checkpoint. The same goes with boss fights. Cuphead doesn't do that. You do have infinite lives, but there are no checkpoints.
The key to beating Cuphead is mobility. You always need to stay on your toes and expect the heavens to open up to smite you in every turn.
You will die a lot in this game. Though you can upgrade your standard 3 HP character, the drawback is you do less damage. You'll be able to purchase skills and new weapon shots in shops within the islands with coins that are found both in the over-world map and non-boss areas. But that's the least interesting bit about the game.
Let's be clear: Cuphead is definitely for anyone who wants to play a challenging game. But even if you aren't that type of gamer, it doesn't mean you shouldn't try Cuphead. It has its own mental and emotional rewards, plus the latest update of the game includes an "easy" mode - so you don't have to git gud playing it.