Well, a otome game well known for its tragic ending is Virche Evermore-ErroR:Salvation-
Fundamentally, it has to experience the bad ending (despair ending) before can reach the happy ending (salvation ending), I could really feel that the developers put a lot of effort into the theme of despair. As for downsides, the long story and the inclusion of cruel, gory elements might be polarizing for some players.
I'm hesitant to go into detail because it might be a spoiler. Personally, I liked Mathis Claude's story