If you liked Darkest Dungeon, you'll probably like the idea of Color of Madness. To be brutally honest, I hyper fixated on Darkest Dungeon for a couple months grinding my heart and soul out and I definitely wasn't amused by an endless mode. For me it meant grinding for hours for trinkets that didn't do anything particularly special, to see my town get buildings that didn't actually appear on the screen and just were in a separate tab to show they exist, to see the same background rooms over a new dungeon, buckled in really just for Lvl 5-6 heros realistically, to play for achievements. I did really appreciate that the worst part of the game play, literally just walking fight to fight, was taken out as you just go to fight after fight.
It's a few extra trinkets, a kind of tossed in story to justify why it's there, and an excuse to push yourself to get a higher and higher number of kills as a personal goal. I mean that literally, because there isn't a leaderboard or anything despite the game using online elements for other DLC(Butcher's Circus). I personally wouldn't get this unless it was on sale, but maybe you like Endless Mode for games more than I do. It's a positive review because I can see it fitting for other people pretty well, just not for me(I might also just be burnt out! Haha).
Generic tips and tricks for the interested:
-Endless mode seems to treat 'Uses per battle' for abilities weirdly, they didn't refresh for me on a rest. May be a bug, very important for me to write out
-The setup is different from the dungeon and doesn't seem to like a lot of mixing when it comes to the team. Unfortunately, my favorite team ended up being Sheildbreaker(DLC) x2, Jester, Vestal. Leper or Man-At-Arms is good too
-Be careful of the trinkets you bring