A lot of Solas posts on my dash, so I’ve been thinking about stuff. (By which I mean: here is my admittedly biased and personal take on Solas and his character over the course of the game.)
Mostly it’s about how well Bioware played his entire character, in terms of replayability, because the stinger scene forces us to re-evaluate his entire character from the perspective of this new information, so if you went in blind on your first playthrough, the second playthrough can be a different experience.
I know it was true for me, because while on my first playthrough I was convinced that Solas was hiding something, I assumed it would be revealed at some point (during a personal quest, or when his approval was high enough). Even once we reached the end and he skedaddled, I was still utterly convinced something was going to be revealed, though I definitely did not expect that.
So in my second playthrough, I paid attention to Solas in a completely different way. I was still filling in blanks, but now I had more information and a vague idea of what those blanks were. And not only were hints and details that I found suspicious in my first playthrough being seen in a new light, but even things I hadn’t even suspected were important were all of a sudden taking an entirely new dimension!
Unfortunately, due to the nature of Solas’s character, and the secrets he keeps, his character development is something we largely need to infer.