Have you got 'Transparency Effects' turned on >Settings>Personalization>Colors>Transparency effects - make sure it's toggled on.
Seemingly the transparency effect for the start menu has changed, meaning it's not as opaque as it was. But if you open up any other screen (e.g Settings - Personalisation) you should see more of the transparent effect.
You can also look at changing a registry key/entry to alter the opaqueness. However, I would only advise to change the registry if you are familiar with what you are doing. A simple Google will bring up some solutions to try.
Good luck.