Monster Slayers is basically a worse Slay the Spire.
The premise of this deck-building roguelite is that you are part of a guild of people trying to take down the Big Bad Guy. Your deck and cards are reset on death to the default ones associated with the class you pick (of which there are several), but you maintain any gear you have accumulated, and any Fame unlocks. Considering that gear increases the damage of your attacks, can give you “temporary” cards in your deck (that will persist as long as that gear is equipped), and boosts your HP, these are essentially permanent advantages that you maintain as soon as you collect them.
The issue is twofold.
First, it is physically impossible to actually “beat” the game without several cycles of death and gear accumulation. In other words: grinding. It’s not the grinding that’s necessarily bad, but rather how the game is balanced around it. You will essentially be paired up with monsters that you have zero chance of defeating, not because of poor planning or execution or even RNG, but simply because the game is “balanced” that way. Losing in that manner never feels fun. Roguelikes (and -lites) often feature punishing RNG, but that’s not what’s going on here – you are engineered to lose X times in Monster Slayers, guaranteed.
The other, more important issue is that… the gameplay is simply bad. In Slay the Spire, you get a notification of what the enemy is about to do, and so there is a possibility of some interplay or tactical considerations. Should you try Blocking the damage, or are you free to go all-out Attacking?
In Monster Slayers, beyond a description of what the enemy does in general, e.g. “Vampire Bats can drain health,” there is no real indication of anything. So what happens is that you just play your cards until you run out of cards or AP, and then your opponent plays their cards, and you wait to see if you’re dead yet or not. That’s really it.
There are some other “minor” issues like the game looking terrible, the UI being horrendous and mostly useless, not having a understanding of what cards the enemy is playing (not that you can interact with them much), the music being repetitive, and the act of playing cards not feeling good. For example, the Rogue class has several “Deal N+1 damage, draw a card” attacks, and while it’s fun chaining those together, if you click too quick, you’ll accidentally play a different card.
If you are looking for another Slay the Spire fix, look elsewhere. If not… play Slay the Spire instead.