I don't like their UI.

What if you're playing Fruit Ninja?
Everytime you goto make a swipe, you can either launch the App Specific Menu or the Apps list or Quick Switch to another App (!!!!)

And if you happened to install this on a device like the Sharp Crystal or the LG G2... you're gonna have a bad time attempting to swipe from those slim bezels.

And what if you're using a phone like the S5 and have an Otterbox case. You again won't be reaching those bezels very effectively.

I mean they're trying to build an OS for an ecosystem, and haven't even considered these points.
If it can't serve those use cases, people aren't going to adopt them. Especially in this age of ever increasing screens, decreasing bezels, slimming phones, etc etc.

Canonical are so bent up simply "to be different" that they don't even consider the actual user.
Just because you imitate some features from the iPhone/Android/Blackberry/webOS/etc etc does not make it a "copy cat" or bad design. You can be original while being alike.