The tabs extended to the top of the screen, making it easier to select and switch between them.

In the new one they sort of "float" and it's very easy to overshoot your mouse.

It may seem trivial but it makes a real difference for some people. I find it easier to switch between them using ctrl+tab which isn't ideal, the old UI did a better job in that regard.

Otherwise the design looks smooth, just a bit difficult to work with at the moment