He doesn't fight them the first time they meet because he knows he stands no chance. Then when you come back to save the Barons wife, he says that the Crones aren't there. One of the witch hunters ask him why he thinks that, he answers something along the lines of "Because we're still alive." The Crones are centuries old. The thing under the oak is something related to the Crones (mother?) and it's centuries old aswell. They are way too powerful and everybody I know who played the game says they felt powerless in their presence.
My problem with Eredin is that there is almost no background on him. I mean, we only discover that the Wild Hunt are elves when they are at Kaer Morhen. Prior to that they seemed like spectres. If there had been more background information on the Aen Elle and Eredin, it would've been better. They are not invincible since they are elves - I get that. What I don't get is that CDPR didn't gives us any more info on them except for that "reveal" at Kaer Morhen. The fight still was underwhelming when you think about how Eredin was their leader but somehow weaker than Imlerith. A leader should be stronger than anyone else under his command, because that's the reason people let him lead.
The White Frost isn't explained enough in Witcher 3. Once again, I understand that it has to be stopped, but I would've liked a more fleshed out writing of why it has to be stopped. I mean, the White Frost won't hit the realm of the Witcher world for another two thousands years IIRC from books. So there was enough time to think about it and make not-so-reckless and rash decisions as Ciri made. Especially after the Hunt was defeated.
I don't think it should feel like the end of his life, quite the opposite. It should just feel that the story ended. CDPR said that this is the last Witcher game where Geralt is the main character. That's cool. But I'd loved to hear more about how he lives, if he meets with the others from time to time, if he sees Ciri again and such. Like some kind of "final goodbye" like ME3 did when you went to every squad member prior to the final battle on Earth and made a final talk (granted that his is another context because it basically IS the final battle of Shepard).