It's immediately clear why this game is so beloved: a roguelike based loosely on Castlevania's classic entries like Symphony of the Night and Aria of Sorrow? Yeah, okay, say no more fam. I'm in, you got me. Throw in some actual Castlevania licensed content and you got yourself a good goddamn done deal in my book.

That being said, I found the endeavor a bit repetitive and just a touch too difficult. I kind of hit a wall after reaching the first run's final boss and was unable to beat any of the other endpoint bosses despite reaching them multiple times. This hard stop to my progress caused me to put down the game indefinitely, but I might come back at some point - cause when the game's good, it's damn good.

Every positive thing you've heard about this game is probably true. It's fun, addictive and hard as hell. I'll never be one of those who can do a no hit-run on 5BC, but that shouldn't discourage you from trying this game. Especially since they've included custom and assist mode, which let's you experience the whole game and tailor the difficulty precisely to your level.
The DLC's are also higly recommended.

Given the gameplay loop I don't think Dead Cells is a game you "finish" on a set date, because it's very easy to make another run if you have some minutes to spare.