This new one is really hard to navigate. I'm having trouble to even go to the last post of a thread. The infinite scrolling thread is terrible. At least give us the option to change skin to the old one.
Not a new UI or skin, it's a new platform. They're using Discourse (www.discourse.org)
To get to the last post of a thread, click on the little record counter in the bottom right (current / max) and tell it to go to max.