Let me start by saying I am not a fan of actually removing features so I don't agree with what they did there. However, with the exception of removing manual WB control, scene modes ect, I can't understand why anyone would like the old UI better than the current one. But to me the details of UI and how you change modes ect..are all secondary to what is by far the most important change:
They FINALLY show a proper 100% preview image instead of a cropped image preview. It should always have been like this. They should never ever have had a cropped image full screen preview in the first place. That is why it is hilarious when I see people actually complaining about the the big black bar for the shutter button area, or that the preview doesn't use all the screen. There is NO WAY for the preview to use the whole screen and actually be correct because the sensor is a different aspect ratio than the screen. As a photographer myself it is so relieving to finally have the exact framing you will get from the final picture shown in the preview. That outweighs all other changes for me.
I would be fine if they were to add an option to display a full screen cropped preview if someone really wants to use it that way (why?!)....however the way it displays the preview now should be the default behavior.