I just finished it too. 
To be honest, I'm not sure where I stand on Briala, but before you get mad at her for "turning on her lover," I would remind you that Celene wronged her first by murdering her parents. And Briala does have a point; Celene would sacrifice her people if it meant stabilizing the Empire. On the other hand, I feel that at least Celene would try to better the situation of the elves whereas Gaspard would stick with the status quo. All I really know is that I can't wait to see Orlais in DAI. I hope we get to meet both Celene and Gaspard.
I know, Celene is certainly not an angel. But wow, Briala pulled Celene so close for that final moment, knowing what she was going to do. Then she drew weapons against her own lover. And when she asked Celene for an exact plan on how she was going to free the elves, was that just a rhetorical question or was she truly open to a quick reply on Celene's part?
Also, didn't she imply that she had partially been in love with Celene because of the magic her ring bestowed upon her? Like, wow. Major cold. I know she didn't know what that ring did or anything, but just saying it...
I just feel so betrayed~ XD
I wonder when, exactly, she decided to betray Celene. She seemed to still believe in her when they were walking through the eluvians. I guess it was when she was thinking about when Celene could have gotten her ring?
And yeah, I'm sure Briala knows Celene is much better for the elves than Gaspard. But her plan isn't to side with Gaspard, she'll just screw both sides over for her own benefit. I wonder though, if Celene really went forward with freeing the elves (perhaps we can reaffirm her to go for it in DAI?), would we be able to get them back together? Kiss, make nice, forget anything ever happened? X)
There were so many hints that Celene and Bria weren't gonna end up together at the end of the book. But then things kinda just calmed down and they started talking again, etc. I was sure things were going to turn out fine between them at that point. Then I remembered that Bria still hadn't used Michel's favour yet and I just realised that there is no way that wouldn't come up. And then things happened.
Wow I still feel like crap XD
You know, my first thought was that was Morrigan at the end who killed Falassan. But it could also be Flemeth. From Witch Hunt, I see that Morrigan can travel through an eluvian, but I don't know how much she can really use them. And I have no idea if Flemeth can or even desires to use them. At this point, I'm leaning more toward Morrigan. 
Morrigan didn't seem to control her eluvian very well. It makes sense that she'd want full access. Seems a bit harsh for Morrigan to kill Felassan, though.