I've been using the "Modern UI" on my WP7.5 for just about two years now and like it better than both the iPhone and the Andriod. It's different and everyone I show it to remarks how fast it is compared to their phones.
As far as Windows 8 goes, it's different, but it has not caused me any issues yet. If you are running it on a desktop or laptop, then it will be easier to use with a scroll mouse. You can navigate the start screen and all list simply by rolling the wheel on you mouse, it's that easy.