I also like the “what’s new message-by-message” view, but I’m an old dog and slow to learn. Also, I’m slow on the forum so whole topics can blow up and blow over between my visits, and this view starts with the latest messages.
Fortunately for me, the old view is still there as it was:
Instead of clicking the “What’s New?” button at the top, click “New Posts” under it.
Or,
Click “What’s New?” and then the “New Posts” item, second from the left in the line under the buttons.
Now I’m going to hop into my time machine to see if the current default “Activity Stream” was always available and this is simply a change in the default view…