I'm in the camp of "everyone should calm down and give it time". As others have said, the new update is only a couple of hours old, but a few users are getting upset about the change.
Whilst I'm running into bugs here and there, I personally enjoy being able to instantly know when I get a reply to a thread though I'm on mobile, and I really enjoy the simplicity of mentions!
I'm sure the devs are hard at work at importing some of the more useful features of the old site, so again, give it time!