Typically, I have already forgotten what the old forum was like. Am I imagining it or did the old form tell you who the thread-starter was on the list of threads, not just who last posted to it?
Weird, I was happy to collapse the wasted space on the left, I just click "forums" on the top when I want to see the forum list.
But that now takes you to a whole new page. It's reminiscent of the problems poeple had with Windows 8 and 'metro', where you get jolted out of the context of what you are doing in order to go to a full-screen menu, rather than the old pull-up/drop-down start menu. There's a fairly big gap on the left of the forum thread, just stick a smaller version of the fourms list in there. Even as a drop-down menu.
I don't know, I'm getting old, I suspect everything I dislike about current UI practice is because it's now all about tiny-display touch-screen mobile devices. I'm a desktop dinosaur.