Unfortunately, you can't get the old one back, but, there is a way to load the basic HTML version of G mail and make this the default every time you log on. Whatever they do in the future the HTML version should always stay fairly basic and straight forward because it is there for low bandwidth/data rate connections.
Log out of G Mail, log back in, quickly, when it is loading, click on 'load basic HTML version' in bottom right hand corner. You will then find that a version, very similar to the old will load.
That's what my partner has done for me and so far it's working.
Best of luck, I know how you feel.