For those wondering how behave Solas with inquisitors he doesn't really like and why some guys might not like him ( though I suspect that those who literally hate him, it's mainly because he is a ' bad guy ' who lied to the protagonist from the beginning, because people at the end learned his genocidal plans, and we know how genocide is unpopular regardless of the reasons, and the fact that Solas can be so ruthless, not even willing to save the elven people from this time. Also the fact that he sees everyone as mages tranquilized , not something pleasant to hear lmao ) :
Solas is not really tolerant with different opinions he disagrees with while he likes to throw some accusations about our narrowness, he is often judgemental about others folks, and he seems to like patronizing as well. He can be quite agressive and haughty sometime, getting emotional even when he tries to use reason to convince the inquisitor. Obviously, it's his passion that consumates him, but it's still can be considered as annoying by other folks.
For example, by just asking a neutral question to Solas, just being curious, he automatically decided to answer with hostility or sarcasm, and I do not think that I lost so many approval points at that point to deserve that tone. My inquisitor just wanted to know more about him. Even before asking him some questions, by just talking to him, Solas can bring himself a subject in an agressive way. With Blackwall, Cassandra, Varric, etc, unless you have a very low approval from them, ( I don't know ), it doesn't happen.
Solas is probably like Vivienne and Morrigan, he can be quite difficult once you disagree with his opinions and ideals, once you lose his respect. But I suppose he is as lovely when it isn't the case. 
I love Solas as a character by the way, I love his voice, I absolutely love his design, so I have zero grievances against him myself, as a player, even if my inquisitor would be glad to punch him. I hope we'll see him again, and I really hope that the inquisitor will be able to deal with him and not the new protagonist, at least his point of view would be cool.
Now, I'm just being honest with what I noticed ( about his flaws ) in my playthrough, I might be wrong though, but this is my opinion.