Earlier quoted context omitted.
The most frustrating change for me was FB (or Messenger later) used to send me an email when I received a message, with the message content inside the email. A few years ago they removed the content from the email and forced me to log into FB or Messenger to see the message. It's extremely user hostile.
It's basically turning your friends' messages into clickbait. I got one recently that was "Someone just flagged me down at a..." and it just feels like a really insidious way to get you to go to Facebook and read the rest. It doesn't even show that much in the actual email, only in the Gmail preview - it's just a link to Facebook (the text is set to "color:#FFFFFF;display:none !important;font-size:1px;").
Something that nearly any other company would have been banished to the spambox for.