Let's see...
- No more daddy or mommy issues that make the love interest seem weak/emotionally unstable
- Not having romances fix whatever issues the characters have
- Make romance a relationship between two equals, not have the LIs worship the hero like a schoolgirl
- This is not going to appeal to many people but: no more romances with aliens that should be goddamn toxic to the protagonist and/or physically totally incompatible (looking at you, Garrus and Tali)
- No more formulaic flirting with a sex scene as a reward before the endgame, be more like DAO
- Don't make squadmate dialogue shut down when you reject them
- Make dialogue reflect being in a relationship more, don't use exactly the same lines for friendship and romance, use words of affection, teasing
- Have your crew acknowledge the relationship
- Don't make the romances only about sex and being in love, have them bond over other things than finding each other hot
- Would be cool to have the option to choose a background for your PC like Shepard and then have that background open up a certain romance option (they could have done that wonderfully with Jack and Mindoir femShep...)
- Make characters unromanceable if your character's personality doesn't work with the LI's personality (Liara and full-blown renegadeShep? Please.)
- Have LIs break up with your character if you insult their core values repeatedly
- Stop with the virgin fantasy
- For male LIs: please stay away from too much gloom and doom and heartbreak
- Very personal request: give me male Liara, somebody deeply loyal but independent and affectionate (kinda like Alistair with more confidence). Emotionally stable! Not a guy with trust issues, self-esteem issues and/or depression (Kaidan, you turned into such a disappointment)
- Or: give me straight Dorian and somehow keep the sass. Or somebody like Joker. A FUN GUY who's committed.
That would be my personal list.