The new version of Firefox uses the Quantum engine. Here you can see the memory usage of Firefox compared to other major browsers:
Firefox's got a redesigned interface with a clean, modern appearance, consistent visual elements, and optimizations for touch screens. I would say that now it looks more like the Windows 10's browser Edge (or let me say, metro design) which is positive I guess?
From what I've said before, Firefox is indeed 2x faster than the previous versions and a bit faster than other browsers. There's one thing though. I think that it is going to be more noticeable on higher end computers as It's speed is mostly optimized to use the available power of them. But, only time will tell if that's true or not.