You fell in love with a game and it's characters, sunk hundreds, maybe even thousands of hours into it. It became a comforting, immensely satisfying part of your daily life. Then you heard a sequel was coming and got really hyped but when it came out it was utter rubbish...
One thing that really threw me off FO4 was the voiced main character. They had to simplify the dialogue options significantly, and I just don't need my character to have a voice, my imagination can sort that out just fine. That way I can make up my own mind about how my character sounds in my head, have more detailed dialogue options (like FO:NV), and not have a locked in boring voice with boring dialogue options. Lots of cool additions in FO4, but it just seemed so shallow, I stopped playing quite early.