My biggest gripe is that I can't easily create folders or hubs of my own and place tiles for those on the start screen.
So, if I have an application suite, like Adobe Creative Studio, Microsoft Office, or Autodesk's products, I end up with a cluttered Start Screen.
In the Start Menu, they would be in folders. Clicking the folder would give me a list of the contents, which I can quickly select.
If I could make a change to the Start Screen it would be to give the user the ability to create custom hubs. Almost like how the Store is structured. Where I can organize my tiles by category, and I could click something if I want to access the contents of the hub/folder.
It's still slower than the Start Menu, but it beats an extremely cluttered Start Screen. And it works with touch.