Now when you login to the Google AdSense console, you will be taken to the new interface without a link to "return to the old interace."
There are many many complaints about this in the WebmasterWorld forums.
Personally, I switched over to the new interface years ago. But many did not and now have no choice. One publisher said:
Google needs to put a giant banner over the employee entrance -
"Just because you CAN do something, does NOT mean that you should."
Rather than -
"Let's try everything - something might work."
Another publisher said, "That ruined my afternoon!"
Anyway, we had two years and Google was very transparent about the switch over.
Forum discussion at WebmasterWorld.