First season was mostly ok, there were some "representation" changes but not too bad. 2nd season they changed everything to the point that it's easier to list what didn't changed. And they changed it for worse... Third season is supposedly so far off that the main actor Henry Caville who is a big fan of the books resigned.

Imagine Peter Jackson made Sam betray Frodo and sell him to Saruman, Gandalf was actually trying to turn Frodo into an orc, elves were actually going to the middle earth not escaping it, and the big bad wasn't Sauron but some new character invented by Jackson that makes no sense but sounds vaguely Icelandish because we want to keep the Nordic theme. Oh and half the party gets killed in Rivendale by the new villain mindfucking Frodo.

And magic stops being unexplained and mythical. You just gather shiny rocks and you can cast spells.

This is roughly equivalent to what has been changed in season 2. Characters and motivations are unrecognizable, the world is a mess.

Season 3 is widely boycotted by fans.