Wait till "Time of contempt" then you will see her true color. As for Yenna, do read "a shard of ice", it is beautiful.
Are you saying it's going to get worse? Oh maaan... lol I don't want to hate her! I did read shard of ice, I've read the first two books already. I'm reading them by the correct order.
Have you read the short stories? Yen is also your average power abusing mage. Geralt is better off alone.
I'm not saying Yen is any better than Triss. But from things I've read around the internet, I always got the impression that, relationship with Yen: pain and abuse everywhere. And relationship with Triss: happiness, fluff, etc. But it's not that simple. There are moments where Yen can be mean and selfish but there are also moments where she can be sweet and loving. I mean, yes, his relationship is way more complicated with Yen because of her complicated personality but in the end they love each other. While with Triss, she just seems desperate to get Geralt in bed when she knows he doesn't want to. It's just... weird and I was not expecting it, I guess. And from what I'm seeing, Yen gets a bit softer after meeting Ciri, not sure how it will affect her relationship with Geralt but I can only imagine it will improve. I guess I'll have my final opinion on this once I read all the books. Either way, I'm excited!
edit: I feel like they made Triss more likable, sweet and innocent on the games and made Yen just as she is on the books and that of course will have people who don't know the whole thing care more about Triss and think Yen is a b*tch. But as I read through the books I'm starting to think she's just as bad or even worse than Yen.