There are really two main reasons people hate it -
1. They don't like the direction they went in with Luke's character, especially since he's so different than he was in the OG trilogy
2. They feel hate that Snoke was killed off so quickly without even getting a backstory
There are also some alt-right types with their SJW rhetoric, but they hate any movie with a significant number of characters that aren't white guys so I don't take those complaints too seriously.
1. They don't like the direction they went in with Luke's character, especially since he's so different than he was in the OG trilogy
2. They feel hate that Snoke was killed off so quickly without even getting a backstory
There are also some alt-right types with their SJW rhetoric, but they hate any movie with a significant number of characters that aren't white guys so I don't take those complaints too seriously.