As far as changes, I mean Joey Batey is great as Jaskier and we got that great song from him in Episode 2. Now, if you don't like Jaskier fine but I think having Jaskier create a song that basically changes what really happens in order to glorify Geralt and give the common people a good story he can profit from, I find that fascinating. Now, I highly disliked the abrupt ending of Episode 2 and how they removed a major part of that story and basically it's whole resolution from the book. But the ending with Jaskier creating this great song, that's basically fake news, was amazing.
The stuff with Ciri in Brokilon just felt like a bit of a goofy diversion. I don't think they did a great job with Brokilon, the Dryads or the Dara character. Once Dara started opening his mouth, his acting and delivery were really goofy. Makes no sense that the ultra paranoid Dryads would let a human male into their village without making him drink the waters either.
Also the conclusion with the Doppler subplot was also iffy. I like that they incorporated a doppler into the story, but the way it was done felt sorta pointless. Just an arbitrary way to move the story along.