I'm adequately obsessed to weigh in on this one.

First, I love this character - and I'd like to see him more fully implemented. In most of my games I'm full of tadpoles, so that's where I stand. But there are important faults in his execution. I agree with everyone who says the tadpoles should matter more. My not-tadpoled game hasn't progressed that far, but I guess there can be a wisdom check if you want to refuse the astral-touched after you've been using the regular tadpoles. That's something, but maybe it should also be easier to get along with the gith if you're not totally tadpoled up. It feels like they would know what you've been up to.

I'd like to see a redemption arc for him, though he probably can't get to 'capital G good' status. He absolutely deceives you in the beginning, but he's also right - the first mindflayer you saw, you crushed its head with your boot. It's fair to think you might not have been open to hearing his case. And all your companions deceive you at first, some more blatantly than others. Astarion seduces you for protection, and has dragged hundreds of people, including actual children, to Cazador. He says he was compelled, but he did resist once - to his enormous detriment, so he did not do it again. But if the 'high road' for the Emperor is to allow his friend to destroy him, surely Astarion could walk into the sun - but none of us want that. People believe Astarion has regrets when he says he does, but not the Emperor. They are both proven liars, as is Gale (a bomb), Shadowheart (cleric of a death cult), and to a lesser degree, Wyll (just has a contract with a devil). And we know that the Emperor and Omeluum are both capable of positive emotions: 'a tickle of mirth' and actual 'joy', respectively.

Finally, there needs to be some consequences for your 'intimate' decisions. There's no way Astarion saw that, even in a dream, and says nothing. Even if you are just friends. Especially if you are just friends. Any commentary he would make toward the Tav he has a close friendship with after he/she/they did what they did would be glorious. And deserved. But don't cheat on him with the squid, is all I'm saying. He deserves better.

TL;DR: I am, in fact, probably a thrall.