For me it's Collar x Malice. It basically set the bar for what I consider a "passing grade" for an otome game. It's really well balanced overall. Not every part is perfect and each aspect has its flaws, but each one also has something that really shines. So now if a game's story is more boring...
Definitely the plot for me. A interesting story is what keeps me awake (I play at nightzzz) and actually makes me want to keep playing. It also helps me really understand the characters, like why they act the way they do. Without that, the romance just doesn't land for me.
Honestly, it's the sim-style ones for me. The Tokimeki Memorial Girl's Side series and the La Corda d'Oro series are the ones I keep coming back to. There's so much random dialogue in those games that I still stumble on lines I've never seen before, even after countless playthroughs lol.