Few of my favourites are long. I also like LONG games and looking for more.
(not including VN, where I consider them not games you play, but games you mostly read and few choice options)
Wicked Rouge, is very long if you want to grind for better stats. like days and weeks long. The new version is shorter at the moment (also the training has become shorter)
Cost of Survival, can be long, still long even for story mode.(since there is no skip days)
Haramase Simulator, also grind yet fun, very long.
Brother King, also very very long, grind.
Strive for power, grind very long.
Treasure of Nadia, also long hours.
so many more where I spent days and weeks, where I am actively involved and mostly fun grind.