So, Salt and Sanctuary? I could tell you it's a 2D Dark Souls with platforming, and that would be an excellent description. There's a bunch of games that mimic the Souls games, but I feel this one does it better than any others I'm aware of. And of course it's not just about the difficulty. It's a highly non-linear 2D action RPG with a bunch of platforming thrown in the mix. And if you've played any of the Dark Souls games, then you'll find the level design, combat, progression, and other mechanics feel very familiar.
I can't help but compare it every step of the way. While it obviously lacks the benefits of the third dimension, which plays a huge role in combat, but also in what I feel is about the only other thing this game is missing in comparison to Dark Souls - the gorgeous views and feeling of scale. You can only do so much via a layered background, but you can never go through a doorframe and take a few seconds just admiring the view, because you can't see ahead of yourself much.
But it may have even outdone its source material in other aspects. Honestly, I found the level design much more intricate, tightly packed, and interwoven, which felt really awesome, like everything's just one big place, not a series of connected areas.
The combat felt to be of a more consistent difficulty, the leveling system forced a bit of variety due to having a skill tree, which was mainly composed of stat upgrades, but also nodes that were required for wearing equipment, or that gave you more health/mana replenishing items. The weapon and armor variety was also decent.
About the only points of criticism I can think of right now, is that, one - combat didn't have much of a vertical aspect, especially since you had no way of avoiding damage while in the air, so jumping was often punished. Two - the last third or quarter of the game felt a bit rushed, having mostly bosses and platforming, with no or next to no enemies. And three - some very important aspects of the game weren't explained nor demonstrated.
About the last part - I played through half the game without knowing anything about weapon crafting, NPC bonuses, fast travel, upgrading, and possibly some more stuff. While I'm not a fan of tutorials, this should probably be made more obvious to players.
But overall, I really liked it, as is evident from spending 30 hours on it in a relatively short timeframe. If you like Dark Souls, I can almost guarantee you'll like this too. But even if you don't, you might still not hate this game. And if you want to spend even more time on it, there's NG+, as well as plenty of secrets and hard-to-reach places.