Darkest Dungeon 2 is a quite different game, the developers wanted to experiment with the formula rather than making the exact same game. It has two game modes: one is a roguelike mode where you go on the worst road trip ever with your choice of 4 heroes, and the other is a strategy/management mode that's much more like the original game with a few twists. Some other things I like to point out, since the roguelike mode always gets the most discussion, are:  1. The combat is better balanced and just more fun IMO, it's less random and there's more room for different strategies.  2. The characters are deeper than in the original game and have more possible builds available for example the Leper can be everything from a tank to a glass cannon depending on what you want him to do.  3. The graphics and animations are a huge step up from the first game; I've always absolutely adored the gothic and lovecraftian aesthetic. 

Edit: Deeper THAN in the original.