The Metro UI is not crummy.
It's actually very powerful, there are a lot of things the MetroUI can do that the start button simply is not capable of doing.
One of them is Search.
You can setup Search Federations in Win7, sure.
Windows 7 Federated Search Providers - Windows 7 Help Forums
Sure looks easy,,,,, not!
This is not an issue in Windows 8 Searching.
Super simple and integrated without having to to do anything but enable Suggestions.
Finding and opening Software and Apps from search is faster than hunt, peck and click.
But that is only a simple part of what Metro can do.
Live Tiles give ultimate access at a glance for so many things it is not even funny.
There is more to MetroUI than just a screen.
This is not to detract from ClassicShell which has it's place. But I find myself using it less.
Hit Win+S and type anything and I don't have to my hands off the keyboard to get at something else to click on
start mouse over stuff, find it, and mouse over something else, and then finally click on the app I want.
The start button is a fairly out dated concept, in it's current configuration.
It can be improved upon, no doubt, and maybe that would make it more functional.
But as it stands, the MetroUI offers better value over all.
It could be said that you do not need MetroUI for the search functionality in Win8.x, true, but as I stated before.
Getting to stuff from there is a lot easier and faster still, then the over all Start Button of old.