Another user said they may have since improved the changes, so I'll have to check it out again. But originally the main interface was a list-style of recent or relevant stats shown, clicking would bring you to more in-depth stats. Most of the time all you needed was the main screen. They swapped that out for a grid of small widgets that showed less data, and you could only choose a few. Clicking would bring you to a stats screen but with less info than before, and often requiring clicking even deeper to find common items.

So lack of customization, and lots of deep-navigation. Garmin's initial action was silence, eventually they said to get over it its not going back. Apparently it got poor feedback in Beta too, so this was just a change they decided chug through with despite a very large outcry on their forums.