My only complaints about Halsin that I actually want to see fixed are:

1. It would be nice if the player could tell Halsin they personally don't wish to date others, but it is okay if he does so (so that if the player doesn't want to do it themself, they can still have that boundary, while still respecting this fundamental part of who Halsin is and not demanding he change it for them)

2. Halsin's sexual assault. It has been addressed many times already, but I think it's the bare minimum that Halsin's sexual assault should be treated AS a sexual assault by the narrative. The way they continuously have Halsin insist he enjoyed it is so beyond hurtful, especially because he also intersperses it with comments that imply Stockholm Syndrome, but are not treated as such. If he feared for his life while imprisoned, it was by definition IMPOSSIBLE for him to give consent- every action he made was under duress. Even if he WASN'T (and he says he was), there is a reason it is in real life considered impossible for prisoners to consent to sex with prison guards. The power imbalances mean that meaningful consent is impossible.

3. I wish we could go with Halsin in the ending. Especially if this could include the player's other love interest, if they have one, coming with them. I could see Karlach being delighted to help out the kids after her engine is fixed, Astarion could be offered protection from the sun, and Shadowheart would just be over the moon to finally get to climb Mount Halsin herself.

Everything else is either perfect or minor enough that I don't think it really needs any changing.