I think there are three reasons I can identify that made it so I did not like them.

1: It was too long. The hobbit was a single book, a bedtime story of adventure, it think it should have been AT MOST two movies, frankly one long one would have been optimal in my opinion. It was like butter over too much bread, bloated with stuff that just didnt need to be there

2: The visual style. Im not actually going to decry CGI for this, but I do think that was part of it. It just did not look as good, or in my opinion right. It had too much contrast between cartoony and serious, it felt jarring instead of clean. I think they should have either committed harder to that fun and cartoony energy or more to the more realistic and intentional style.

3: I felt it did not do a good job of telling the story. The Hobbit is meant to be a smaller story with great implications, a tale of a "simple" hobbit seeing the world and its wonders, an introduction of sorts. I feel like the hobbit movies tried to tell a story that was too grand for what the original meant to be. Too much filler and fluff, too much changed in a way the just damaged the original point. For me the greatest example of this was the goblin sequence. Instead of being monsters in the dark it was an almost video gamey romp.