Shadowheart's personality is fine, the realistic and "pragmatic" point of view in a fantasy situation complete with tentacle faced brain gobbling psychics is mildly refreshing even. That being said her nigh on constant disapproval of the overwhelming majority of my actions and choices is bloody irksome.
For instance there I am taking on a quest to help a bunch of refugees, feels good like doing the right thin- Shadowheart disapproves... Oh hey there's that fighter who helped me out on that ship Sure i'll help get her out of that cage-Shadowheart disapproves ...
Even Lae'zel who is vicious, ruthless, malicious and borderline sadistic at times is easier to get along with...
Astarion the murderous psychopath vampire just as easy to get along with strangely while even staying in the good graces of Gale and Wyll.
These things do not really factor into combat though I will say they do factor slightly into how I feel about bringing any of them along as at the very least Lae'zel and Astarion can back up those negative tendencies with the ability to really make good on them. Where as Shadowheart just kinda sits there judging me for not being an opportunistic self serving jerk, only to prove themselves of overall "okay" combat value later on. which doesn't exactly buy a lot of care or respect from me.
Her personality is a bit erratic since there are times where she joins the Lazael and Astarion club of selfish assholes where they disapprove when you help someone, but at other times she approves.
Lazael and Astarion are pretty consistent in always disapproving when you help people.
The only time I saw Lazael stop for call of help was during the burning building where you get the diplomat and the other guy out of the building to send you to search for the duke. Lazael will remark people need help and the building is on fire.
All in all, the two spiteful thots and the petty ponce really do compete with each other to be sociopaths, but the petty ponce hands down beats the thots in consisdent disregard and disdain for others despite his sob story about being a victim.
Can't wait for Daddy Halsin to join the party and for fighters to not be essential for the party to function and spell casters being less trash, so I can run the Wholesome Bros troupe without the annoying selfish twats and not handicap myself by doing so.
Because right now if you're not using Lazael, you're seriously gimping your party because of how broken fighters are for both damage and threat control. At least Shadowheart you can replace when you get Staff of Arcane Mastery to give yourself the essential Bless to not miss half your spells.
Romance is the primary thing for approval but if your approval gets low enough, I *think* they will bail on you. Never put it to the test myself. Dunno if Larian will come up with any other mechanics for it. Probably/may also influence their willingness to unfold their personal stories as well.
I don't know if that's the case, because I certainly forced Lazael to back off in any aggressive dialogue and didn't give a damn about her disapproval, and she was still around and apparently happy with me during the Tiefling party. And since I only play good aligned PC's, naturally Astarion disapproved every single decision I took. I've been seriously tempted to sell him out to the hunter in the swamp on this playthrough, but I can't bring myself to do it just like I can't push Lazael off the Nautiloid after looting her armor (plus that would heavily gimp my party, because again fighters are super OP alongside rogues).