Every once in a while RNG is going to take you to the woodshed. Crit, then crit again, then a big DOT, then it's goodbye to the best Vestal you ever had. That's RPG though. Disasters can be mitigated, but never banished.
The maps are too repetitive. There aren't many quests. There are a lot of classes, and a lot of ways to staff a party. Customization of individual party members might be lacking, but overall the game offers a lot of variety in play style. Each location is visually unique, and personally I think the art is gorgeous. Lots of cool monsters that vary considerably in appearance and behavior. The bosses "repeating" isn't the most thrilling progression system, but 3 bosses per dungeon seems like a good mix to me.
Valid complaints against Darkest Dungeon are repetitiveness and sometimes really punishing RNG. I find that some of the harshest critics tend to bury somewhere in their review "after playing 100 hours" or "after leveling every class to maximum," and I think, well yes, maybe Darkest Dungeon does start to fall apart after being completely conquered. It's probably not a forever game that can be played over and over again.
I've been playing the early access release for months and think the game is really fun. There are many rogue lites, many turn based strategy games, many 2D games with striking art, many horror games, even the cosmic horror sub genre is well represented! Darkest Dungeon takes elements common in many games, then combines them into a compelling experience unlike any other game I've recently played. I think it's a terrific time and recommend it to anyone who enjoys games that demand a little more from their audience.