I think it depends on other factors. 2DCG is almost always drawn/made from scratch or custom made, whereas 3dcg has a tendency to reuse the same assets etc. If I want to be immersed I'd probably go with 3dcg. 2dcg more focuses around less realistic stories and find it easier to come across.
Dark fantasy yes, horror rather no. For me as a non-immersive player, horror usually just doesn't work, meaning horror games fail to invoke any sort of fear in me. I'm still interested in stories about vampires, werewolves, Frankenstein monsters and other creatures usually associated with the...
personally hate grindy games. just proves the lack of content/story in game. so it is definitely not a must. i came across a lot of games here with sandbox style gameplay but with little grind:
Lucky Paradox
Deluca family
Sins of the father
Milfy day
are a few examples