Monster train is very good. It’s probably a bit easier than others in the genre. It’s more about how many modifiers you use to make the game more difficult than simply finishing. You can generally always beat the game on any given run, you aren’t as dependent on getting the exact right cards or unlocking more powerful cards.
I can’t speak too much to the dlc, I don’t have a ton of experience with it, but my friend has literally unlocked and completed everything and still enjoys the game.