I got it recently too, with no option to go back. However, I was able to go back after clearing my browser cookies for twitter.com
Did it offer you some choice after you cleared out the cookies?
When I cleared my cookies it just went back to legacy twitter automatically
Sounds like a fortuitous bug TBH.
Gonna bet a dollar that in short time, they'll have you back using the sucky new interface :-D
:( that sounds like a nightmare
They've now hijacked 1/3 of screen real estate for useless things I don't want.
This is going to require some browser plugins to fix, isn't it?