I very much preferred the method of "Recent posts" in vB 3.x. It allowed me to check what had been posted recently including my own posts. It also let me go back to the list and see other people's posts that I had seen, but wanted to find again.
I dont like "What's new?". I much prefer "Recent posts". Posts I have read were not bolded. Unread posts were. It behaved consistently with how email and other messaging clients work.
Bring back "Recent Posts". Throw away "What's New?". You can call it "What's New?" if you must, that is OK, but provide an option so that the What's New? tab can operate legacy style.